diff --git a/cmd/kubectl-moco/cmd/completion.go b/cmd/kubectl-moco/cmd/completion.go
new file mode 100644
index 000000000..3defa93e5
--- /dev/null
+++ b/cmd/kubectl-moco/cmd/completion.go
@@ -0,0 +1,49 @@
+package cmd
+
+import (
+	"context"
+	"strings"
+
+	mocov1beta2 "github.com/cybozu-go/moco/api/v1beta2"
+	"github.com/spf13/cobra"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+)
+
+func mysqlClusterCandidates(ctx context.Context, cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+	if len(args) != 0 {
+		return nil, cobra.ShellCompDirectiveNoFileComp
+	}
+
+	var namespace string
+
+	if cmd.Flags().Changed("namespace") {
+		ns, err := cmd.Flags().GetString("namespace")
+		if err != nil {
+			return nil, cobra.ShellCompDirectiveError
+		}
+		namespace = ns
+	} else {
+		ns, _, err := kubeConfigFlags.ToRawKubeConfigLoader().Namespace()
+		if err != nil {
+			return nil, cobra.ShellCompDirectiveError
+		}
+		namespace = ns
+	}
+
+	clusters := &mocov1beta2.MySQLClusterList{}
+	if err := kubeClient.List(ctx, clusters, &client.ListOptions{
+		Namespace: namespace,
+	}); err != nil {
+		return nil, cobra.ShellCompDirectiveError
+	}
+
+	var candidates []string
+	for _, c := range clusters.Items {
+		if !strings.HasPrefix(c.Name, toComplete) {
+			continue
+		}
+		candidates = append(candidates, c.Name)
+	}
+
+	return candidates, cobra.ShellCompDirectiveNoFileComp
+}
diff --git a/cmd/kubectl-moco/cmd/credential.go b/cmd/kubectl-moco/cmd/credential.go
index 0c56e155f..ffc43734a 100644
--- a/cmd/kubectl-moco/cmd/credential.go
+++ b/cmd/kubectl-moco/cmd/credential.go
@@ -21,6 +21,9 @@ var credentialCmd = &cobra.Command{
 	RunE: func(cmd *cobra.Command, args []string) error {
 		return fetchCredential(cmd.Context(), args[0])
 	},
+	ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		return mysqlClusterCandidates(cmd.Context(), cmd, args, toComplete)
+	},
 }
 
 func fetchCredential(ctx context.Context, clusterName string) error {
@@ -47,5 +50,12 @@ func init() {
 	fs.StringVarP(&credentialConfig.user, "mysql-user", "u", "moco-readonly", "User for login to mysql")
 	fs.StringVar(&credentialConfig.format, "format", "plain", "The format of output [`plain` or `mycnf`]")
 
+	_ = credentialCmd.RegisterFlagCompletionFunc("mysql-user", func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		return []string{"moco-readonly", "moco-writable", "moco-admin"}, cobra.ShellCompDirectiveDefault
+	})
+	_ = credentialCmd.RegisterFlagCompletionFunc("format", func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		return []string{"plain", "mycnf"}, cobra.ShellCompDirectiveDefault
+	})
+
 	rootCmd.AddCommand(credentialCmd)
 }
diff --git a/cmd/kubectl-moco/cmd/mysql.go b/cmd/kubectl-moco/cmd/mysql.go
index 44f707182..19e323ed6 100644
--- a/cmd/kubectl-moco/cmd/mysql.go
+++ b/cmd/kubectl-moco/cmd/mysql.go
@@ -36,6 +36,9 @@ var mysqlCmd = &cobra.Command{
 	RunE: func(cmd *cobra.Command, args []string) error {
 		return runMySQLCommand(cmd.Context(), args[0], cmd, args[1:])
 	},
+	ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		return mysqlClusterCandidates(cmd.Context(), cmd, args, toComplete)
+	},
 }
 
 func runMySQLCommand(ctx context.Context, clusterName string, cmd *cobra.Command, args []string) error {
diff --git a/cmd/kubectl-moco/cmd/switchover.go b/cmd/kubectl-moco/cmd/switchover.go
index b0f175488..49bed93eb 100644
--- a/cmd/kubectl-moco/cmd/switchover.go
+++ b/cmd/kubectl-moco/cmd/switchover.go
@@ -19,6 +19,9 @@ var switchoverCmd = &cobra.Command{
 	RunE: func(cmd *cobra.Command, args []string) error {
 		return switchover(cmd.Context(), args[0])
 	},
+	ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		return mysqlClusterCandidates(cmd.Context(), cmd, args, toComplete)
+	},
 }
 
 func switchover(ctx context.Context, name string) error {