diff --git a/contrib/opencensus-ext-ocagent/tests/test_trace_exporter_utils.py b/contrib/opencensus-ext-ocagent/tests/test_trace_exporter_utils.py
index 52de1aa27..5e0231177 100644
--- a/contrib/opencensus-ext-ocagent/tests/test_trace_exporter_utils.py
+++ b/contrib/opencensus-ext-ocagent/tests/test_trace_exporter_utils.py
@@ -16,6 +16,7 @@
 from datetime import datetime, timedelta
 import unittest
 
+from opencensus.common import utils as common_utils
 from opencensus.ext.ocagent.trace_exporter import utils
 from opencensus.ext.ocagent.trace_exporter.gen.opencensus.trace.v1 \
     import trace_pb2
@@ -532,7 +533,8 @@ def test_datetime_str_to_proto_ts_conversion(self):
         expected_seconds = int(delta.total_seconds())
         expected_nanos = delta.microseconds * 1000
 
-        proto_ts = utils.proto_ts_from_datetime_str(now.isoformat() + 'Z')
+        proto_ts = utils.proto_ts_from_datetime_str(
+            common_utils.to_iso_str(now))
         self.assertEqual(proto_ts.seconds, int(expected_seconds))
         self.assertEqual(proto_ts.nanos, expected_nanos)
 
diff --git a/opencensus/common/utils/__init__.py b/opencensus/common/utils/__init__.py
index d8646ecd8..9ed6b0afe 100644
--- a/opencensus/common/utils/__init__.py
+++ b/opencensus/common/utils/__init__.py
@@ -69,6 +69,13 @@ def check_str_length(str_to_check, limit=MAX_LENGTH):
     return (result, truncated_byte_count)
 
 
+def to_iso_str(ts=None):
+    """Get an ISO 8601 string for a UTC datetime."""
+    if ts is None:
+        ts = datetime.datetime.utcnow()
+    return ts.strftime("%Y-%m-%dT%H:%M:%S.%fZ")
+
+
 def timestamp_to_microseconds(timestamp):
     """Convert a timestamp string into a microseconds value
     :param timestamp
diff --git a/opencensus/stats/measurement_map.py b/opencensus/stats/measurement_map.py
index 2c1dab23a..8cdf2fb4d 100644
--- a/opencensus/stats/measurement_map.py
+++ b/opencensus/stats/measurement_map.py
@@ -12,9 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from datetime import datetime
 import logging
 
+from opencensus.common import utils
 from opencensus.tags import execution_context
 
 
@@ -114,6 +114,6 @@ def record(self, tag_map_tags=None):
         self.measure_to_view_map.record(
                 tags=tag_map_tags,
                 measurement_map=self.measurement_map,
-                timestamp=datetime.utcnow().isoformat() + 'Z',
+                timestamp=utils.to_iso_str(),
                 attachments=self.attachments
         )
diff --git a/opencensus/stats/view_data.py b/opencensus/stats/view_data.py
index 52b43d2ab..47adaa33d 100644
--- a/opencensus/stats/view_data.py
+++ b/opencensus/stats/view_data.py
@@ -12,9 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from datetime import datetime
 import copy
 
+from opencensus.common import utils
+
 
 class ViewData(object):
     """View Data is the aggregated data for a particular view
@@ -62,11 +63,11 @@ def tag_value_aggregation_data_map(self):
 
     def start(self):
         """sets the start time for the view data"""
-        self._start_time = datetime.utcnow().isoformat() + 'Z'
+        self._start_time = utils.to_iso_str()
 
     def end(self):
         """sets the end time for the view data"""
-        self._end_time = datetime.utcnow().isoformat() + 'Z'
+        self._end_time = utils.to_iso_str()
 
     def get_tag_values(self, tags, columns):
         """function to get the tag values from tags and columns"""
diff --git a/opencensus/stats/view_manager.py b/opencensus/stats/view_manager.py
index c7c32d0f2..2afaea22c 100644
--- a/opencensus/stats/view_manager.py
+++ b/opencensus/stats/view_manager.py
@@ -12,16 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from opencensus.common import utils
 from opencensus.stats.measure_to_view_map import MeasureToViewMap
 from opencensus.stats import execution_context
-from datetime import datetime
 
 
 class ViewManager(object):
     """View Manager allows the registering of Views for collecting stats
     and receiving stats data as View Data"""
     def __init__(self):
-        self.time = datetime.utcnow().isoformat() + 'Z'
+        self.time = utils.to_iso_str()
         if execution_context.get_measure_to_view_map() == {}:
             execution_context.set_measure_to_view_map(MeasureToViewMap())
 
diff --git a/opencensus/trace/span.py b/opencensus/trace/span.py
index 43130d509..041b597f1 100644
--- a/opencensus/trace/span.py
+++ b/opencensus/trace/span.py
@@ -15,7 +15,7 @@
 from datetime import datetime
 from itertools import chain
 
-from opencensus.common.utils import get_truncatable_str
+from opencensus.common import utils
 from opencensus.trace import attributes
 from opencensus.trace import base_span
 from opencensus.trace import link as link_module
@@ -225,11 +225,11 @@ def add_link(self, link):
 
     def start(self):
         """Set the start time for a span."""
-        self.start_time = datetime.utcnow().isoformat() + 'Z'
+        self.start_time = utils.to_iso_str()
 
     def finish(self):
         """Set the end time for a span."""
-        self.end_time = datetime.utcnow().isoformat() + 'Z'
+        self.end_time = utils.to_iso_str()
 
     def __iter__(self):
         """Iterate through the span tree."""
@@ -265,7 +265,7 @@ def format_span_json(span):
     :returns: Formatted Span.
     """
     span_json = {
-        'displayName': get_truncatable_str(span.name),
+        'displayName': utils.get_truncatable_str(span.name),
         'spanId': span.span_id,
         'startTime': span.start_time,
         'endTime': span.end_time,
diff --git a/opencensus/trace/time_event.py b/opencensus/trace/time_event.py
index aaa6ee49d..2c315fa37 100644
--- a/opencensus/trace/time_event.py
+++ b/opencensus/trace/time_event.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from opencensus.common.utils import get_truncatable_str
+from opencensus.common import utils
 
 
 class Type(object):
@@ -46,7 +46,8 @@ def __init__(self, description, attributes=None):
 
     def format_annotation_json(self):
         annotation_json = {}
-        annotation_json['description'] = get_truncatable_str(self.description)
+        annotation_json['description'] = utils.get_truncatable_str(
+            self.description)
 
         if self.attributes is not None:
             annotation_json['attributes'] = self.attributes.\
@@ -126,7 +127,7 @@ class TimeEvent(object):
                           spans.
     """
     def __init__(self, timestamp, annotation=None, message_event=None):
-        self.timestamp = timestamp.isoformat() + 'Z'
+        self.timestamp = utils.to_iso_str(timestamp)
 
         if annotation is not None and message_event is not None:
             raise ValueError("A TimeEvent can contain either an Annotation"
diff --git a/tests/unit/stats/exporters/test_stackdriver_stats.py b/tests/unit/stats/exporters/test_stackdriver_stats.py
index 7b52744cd..fc3d920e2 100644
--- a/tests/unit/stats/exporters/test_stackdriver_stats.py
+++ b/tests/unit/stats/exporters/test_stackdriver_stats.py
@@ -18,6 +18,7 @@
 
 from google.cloud import monitoring_v3
 
+from opencensus.common import utils
 from opencensus.common.version import __version__
 from opencensus.stats import aggregation as aggregation_module
 from opencensus.stats import aggregation_data as aggregation_data_module
@@ -58,7 +59,7 @@
     VIDEO_SIZE_VIEW_NAME, "processed video size over time", [FRONTEND_KEY],
     VIDEO_SIZE_MEASURE, VIDEO_SIZE_DISTRIBUTION)
 
-TEST_TIME = datetime(2018, 12, 25, 1, 2, 3, 4).isoformat() + 'Z'
+TEST_TIME = utils.to_iso_str(datetime(2018, 12, 25, 1, 2, 3, 4))
 
 
 class _Client(object):
diff --git a/tests/unit/stats/test_view_data.py b/tests/unit/stats/test_view_data.py
index 41c9aaf15..1edf3008c 100644
--- a/tests/unit/stats/test_view_data.py
+++ b/tests/unit/stats/test_view_data.py
@@ -12,9 +12,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import unittest
-import mock
 from datetime import datetime
+import mock
+import unittest
+
+from opencensus.common import utils
 from opencensus.stats import aggregation as aggregation_module
 from opencensus.stats import measure as measure_module
 from opencensus.stats import view_data as view_data_module
@@ -82,7 +84,7 @@ def test_record(self):
 
         context = mock.Mock()
         context.map = {'key1': 'val1', 'key2': 'val2'}
-        time = datetime.utcnow().isoformat() + 'Z'
+        time = utils.to_iso_str()
         value = 1
         self.assertEqual({}, view_data.tag_value_aggregation_data_map)
 
@@ -143,7 +145,7 @@ def test_record_with_attachment(self):
             view=view, start_time=start_time, end_time=end_time)
         context = mock.Mock
         context.map = {'key1': 'val1', 'key2': 'val2'}
-        time = datetime.utcnow().isoformat() + 'Z'
+        time = utils.to_iso_str()
         value = 1
 
         view_data.record(
@@ -193,7 +195,7 @@ def test_record_with_attachment_no_histogram(self):
             view=view, start_time=start_time, end_time=end_time)
         context = mock.Mock
         context.map = {'key1': 'val1', 'key2': 'val2'}
-        time = datetime.utcnow().isoformat() + 'Z'
+        time = utils.to_iso_str()
         value = 1
         view_data.record(
             context=context,
@@ -223,7 +225,7 @@ def test_record_with_multi_keys(self):
             view=view, start_time=start_time, end_time=end_time)
         context = mock.Mock()
         context.map = {'key1': 'val1', 'key2': 'val2'}
-        time = datetime.utcnow().isoformat() + 'Z'
+        time = utils.to_iso_str()
         value = 1
         self.assertEqual({}, view_data.tag_value_aggregation_data_map)
 
@@ -242,7 +244,7 @@ def test_record_with_multi_keys(self):
 
         context_2 = mock.Mock()
         context_2.map = {'key1': 'val3', 'key2': 'val2'}
-        time_2 = datetime.utcnow().isoformat() + 'Z'
+        time_2 = utils.to_iso_str()
         value_2 = 2
         view_data.record(
             context=context_2,
@@ -258,7 +260,7 @@ def test_record_with_multi_keys(self):
         sum_data_2 = view_data.tag_value_aggregation_data_map.get(tuple_vals_2)
         self.assertEqual(2, sum_data_2.sum_data)
 
-        time_3 = datetime.utcnow().isoformat() + 'Z'
+        time_3 = utils.to_iso_str()
         value_3 = 3
         # Use the same context {'key1': 'val1', 'key2': 'val2'}.
         # Record to entry [(val1, val2), sum=1].
@@ -282,7 +284,7 @@ def test_record_with_missing_key_in_context(self):
             'key1': 'val1',
             'key3': 'val3'
         }  # key2 is not in the context.
-        time = datetime.utcnow().isoformat() + 'Z'
+        time = utils.to_iso_str()
         value = 4
         view_data.record(
             context=context, value=value, timestamp=time, attachments=None)
@@ -303,7 +305,7 @@ def test_record_with_none_context(self):
         end_time = datetime.utcnow()
         view_data = view_data_module.ViewData(
             view=view, start_time=start_time, end_time=end_time)
-        time = datetime.utcnow().isoformat() + 'Z'
+        time = utils.to_iso_str()
         value = 4
         view_data.record(
             context=None, value=value, timestamp=time, attachments=None)
diff --git a/tests/unit/trace/test_blank_span.py b/tests/unit/trace/test_blank_span.py
index da0a2593e..cf8126233 100644
--- a/tests/unit/trace/test_blank_span.py
+++ b/tests/unit/trace/test_blank_span.py
@@ -15,6 +15,8 @@
 import datetime
 import mock
 import unittest
+
+from opencensus.common import utils
 from opencensus.trace.link import Link
 from opencensus.trace.span import format_span_json
 from opencensus.trace.time_event import TimeEvent
@@ -85,13 +87,12 @@ def test_do_not_crash(self):
         span.finish()
 
     def test_constructor_explicit(self):
-        from datetime import datetime
 
         span_id = 'test_span_id'
         span_name = 'test_span_name'
         parent_span = mock.Mock()
-        start_time = datetime.utcnow().isoformat() + 'Z'
-        end_time = datetime.utcnow().isoformat() + 'Z'
+        start_time = utils.to_iso_str()
+        end_time = utils.to_iso_str()
         attributes = {
             'http.status_code': '200',
             'component': 'HTTP load balancer',
diff --git a/tests/unit/trace/test_span.py b/tests/unit/trace/test_span.py
index 90d52684b..9565bfb34 100644
--- a/tests/unit/trace/test_span.py
+++ b/tests/unit/trace/test_span.py
@@ -12,12 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import datetime
 import unittest
 
 import mock
 
 from google.rpc import code_pb2
 
+from opencensus.common import utils
 from opencensus.trace.stack_trace import StackTrace
 from opencensus.trace.status import Status
 from opencensus.trace.time_event import TimeEvent
@@ -56,13 +58,12 @@ def test_constructor_defaults(self):
         self.assertIsNone(span.context_tracer)
 
     def test_constructor_explicit(self):
-        from datetime import datetime
 
         span_id = 'test_span_id'
         span_name = 'test_span_name'
         parent_span = mock.Mock()
-        start_time = datetime.utcnow().isoformat() + 'Z'
-        end_time = datetime.utcnow().isoformat() + 'Z'
+        start_time = utils.to_iso_str()
+        end_time = utils.to_iso_str()
         attributes = {
             'http.status_code': '200',
             'component': 'HTTP load balancer',
@@ -136,7 +137,6 @@ def test_add_attribute(self):
 
     def test_add_time_event(self):
         from opencensus.trace.time_event import TimeEvent
-        import datetime
 
         span_name = 'test_span_name'
         span = self._make_one(span_name)
@@ -320,7 +320,6 @@ def test_format_span_json_no_parent_span(self):
     @mock.patch.object(TimeEvent, 'format_time_event_json')
     def test_format_span_json_with_parent_span(self, time_event_mock,
                                                status_mock, stack_trace_mock):
-        import datetime
 
         from opencensus.trace.link import Link
         from opencensus.trace.span import format_span_json
diff --git a/tests/unit/trace/test_span_data.py b/tests/unit/trace/test_span_data.py
index 8d50843e4..7966f84fc 100644
--- a/tests/unit/trace/test_span_data.py
+++ b/tests/unit/trace/test_span_data.py
@@ -15,6 +15,7 @@
 import datetime
 import unittest
 
+from opencensus.common import utils
 from opencensus.trace import link
 from opencensus.trace import span_context
 from opencensus.trace import span_data as span_data_module
@@ -31,8 +32,8 @@ def test_create_span_data(self):
             span_id='6e0c63257de34c92',
             parent_span_id='6e0c63257de34c93',
             attributes={'key1': 'value1'},
-            start_time=datetime.datetime.utcnow().isoformat() + 'Z',
-            end_time=datetime.datetime.utcnow().isoformat() + 'Z',
+            start_time=utils.to_iso_str(),
+            end_time=utils.to_iso_str(),
             stack_trace=None,
             links=None,
             status=None,
@@ -49,8 +50,8 @@ def test_span_data_immutable(self):
             span_id='6e0c63257de34c92',
             parent_span_id='6e0c63257de34c93',
             attributes={'key1': 'value1'},
-            start_time=datetime.datetime.utcnow().isoformat() + 'Z',
-            end_time=datetime.datetime.utcnow().isoformat() + 'Z',
+            start_time=utils.to_iso_str(),
+            end_time=utils.to_iso_str(),
             stack_trace=None,
             links=None,
             status=None,
@@ -76,8 +77,8 @@ def test_format_legacy_trace_json(self):
             span_id='6e0c63257de34c92',
             parent_span_id='6e0c63257de34c93',
             attributes={'key1': 'value1'},
-            start_time=datetime.datetime.utcnow().isoformat() + 'Z',
-            end_time=datetime.datetime.utcnow().isoformat() + 'Z',
+            start_time=utils.to_iso_str(),
+            end_time=utils.to_iso_str(),
             stack_trace=stack_trace.StackTrace(stack_trace_hash_id='111'),
             links=[link.Link('1111', span_id='6e0c63257de34c92')],
             status=status.Status(code=0, message='pok'),
diff --git a/tests/unit/trace/test_time_event.py b/tests/unit/trace/test_time_event.py
index b38cad87e..b6c616142 100644
--- a/tests/unit/trace/test_time_event.py
+++ b/tests/unit/trace/test_time_event.py
@@ -17,6 +17,7 @@
 
 import mock
 
+from opencensus.common import utils
 from opencensus.trace import time_event as time_event_module
 
 
@@ -137,7 +138,7 @@ def test_constructor(self):
         time_event = time_event_module.TimeEvent(
             timestamp=timestamp, message_event=message_event)
 
-        self.assertEqual(time_event.timestamp, timestamp.isoformat() + 'Z')
+        self.assertEqual(time_event.timestamp, utils.to_iso_str(timestamp))
         self.assertEqual(time_event.message_event, message_event)
 
     def test_constructor_value_error(self):
@@ -163,7 +164,7 @@ def test_format_time_event_json_annotation(self):
 
         time_event_json = time_event.format_time_event_json()
         expected_time_event_json = {
-            'time': timestamp.isoformat() + 'Z',
+            'time': utils.to_iso_str(timestamp),
             'annotation': mock_annotation
         }
 
@@ -181,7 +182,7 @@ def test_format_time_event_json_message_event(self):
 
         time_event_json = time_event.format_time_event_json()
         expected_time_event_json = {
-            'time': timestamp.isoformat() + 'Z',
+            'time': utils.to_iso_str(timestamp),
             'message_event': mock_message_event
         }
 
diff --git a/tests/unit/trace/test_tracer.py b/tests/unit/trace/test_tracer.py
index 58b28bbe1..21a590eb4 100644
--- a/tests/unit/trace/test_tracer.py
+++ b/tests/unit/trace/test_tracer.py
@@ -221,10 +221,7 @@ def test_end_span_sampled(self):
         span.__iter__ = mock.Mock(return_value=iter([span]))
         execution_context.set_current_span(span)
 
-        patch = mock.patch('opencensus.trace.span.get_truncatable_str',
-                           mock.Mock())
-
-        with patch:
+        with mock.patch('opencensus.trace.span.utils.get_truncatable_str'):
             tracer.end_span()
 
         self.assertTrue(span.finish.called)