diff --git a/Substring-without-repeat.py b/Substring-without-repeat.py
new file mode 100644
index 0000000..953a9ae
--- /dev/null
+++ b/Substring-without-repeat.py
@@ -0,0 +1,31 @@
+class Solution(object):
+    def lengthOfLongestSubstring(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        seen = ""
+        current_len = 0
+        longest = 0
+        start = 0
+        flag = False
+        ind = 0
+        while ind < len(s):
+            if s[ind] in seen:
+                seen = ""
+                if current_len > longest:
+                    longest = current_len
+                current_len = 0
+                start += 1
+                ind = start
+                flag = True
+
+            
+            if not flag:
+                current_len += 1
+                seen += s[ind]
+                ind += 1
+            flag = False
+        return max(longest, current_len)
+
+