diff --git a/tools/commissioner_thci/commissioner.py b/tools/commissioner_thci/commissioner.py
index fecd24dc..c9b1c192 100644
--- a/tools/commissioner_thci/commissioner.py
+++ b/tools/commissioner_thci/commissioner.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 #   Copyright (c) 2019, The OpenThread Commissioner Authors.
diff --git a/tools/commissioner_thci/commissioner_ctl.py b/tools/commissioner_thci/commissioner_ctl.py
index f7e7b038..8a4e0cb6 100755
--- a/tools/commissioner_thci/commissioner_ctl.py
+++ b/tools/commissioner_thci/commissioner_ctl.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 #   Copyright (c) 2019, The OpenThread Commissioner Authors.
@@ -30,8 +30,6 @@
 Commissioner daemon controller
 """
 
-from __future__ import print_function
-
 import os
 import argparse
 import multiprocessing.connection
diff --git a/tools/commissioner_thci/commissioner_impl.py b/tools/commissioner_thci/commissioner_impl.py
index 38479e39..fc8c9ebb 100644
--- a/tools/commissioner_thci/commissioner_impl.py
+++ b/tools/commissioner_thci/commissioner_impl.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 #   Copyright (c) 2019, The OpenThread Commissioner Authors.
@@ -194,7 +194,7 @@ def getSessionId(self):
             raise_(commissioner.Error, repr(e), sys.exc_info()[2])
 
     def MGMT_COMMISSIONER_GET(self, tlvTypes):
-        types = ' '.join(map(lambda x: TLV_TYPE_TO_STRING[x], tlvTypes))
+        types = ' '.join([TLV_TYPE_TO_STRING[x] for x in tlvTypes])
         command = 'commdataset get ' + types
         response = self._execute_and_check(command)
 
@@ -252,7 +252,7 @@ def disableJoiner(self, joinerType, eui64=None):
         self._execute_and_check(' '.join(command))
 
     def MGMT_ACTIVE_GET(self, tlvTypes):
-        types = ' '.join(map(lambda x: TLV_TYPE_TO_STRING[x], tlvTypes))
+        types = ' '.join([TLV_TYPE_TO_STRING[x] for x in tlvTypes])
         result = self._execute_and_check(
             'opdataset get active {}'.format(types))
 
@@ -267,7 +267,7 @@ def MGMT_ACTIVE_SET(self, activeOpDataset):
             OTCommissioner._active_op_dataset_to_json(activeOpDataset)))
 
     def MGMT_PENDING_GET(self, tlvTypes):
-        types = ' '.join(map(lambda x: TLV_TYPE_TO_STRING[x], tlvTypes))
+        types = ' '.join([TLV_TYPE_TO_STRING[x] for x in tlvTypes])
         result = self._execute_and_check(
             'opdataset get pending {}'.format(types))
 
@@ -282,7 +282,7 @@ def MGMT_PENDING_SET(self, pendingOpDataset):
             OTCommissioner._pending_op_dataset_to_json(pendingOpDataset)))
 
     def MGMT_BBR_GET(self, tlvTypes):
-        types = ' '.join(map(lambda x: TLV_TYPE_TO_STRING[x], tlvTypes))
+        types = ' '.join([TLV_TYPE_TO_STRING[x] for x in tlvTypes])
         result = self._execute_and_check('bbrdataset get {}'.format(types))
 
         try:
diff --git a/tools/commissioner_thci/commissionerd.py b/tools/commissioner_thci/commissionerd.py
index 7571a800..1ad038ee 100755
--- a/tools/commissioner_thci/commissionerd.py
+++ b/tools/commissioner_thci/commissionerd.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 #   Copyright (c) 2019, The OpenThread Commissioner Authors.
@@ -30,8 +30,6 @@
 Commissioner daemon process
 """
 
-from __future__ import print_function
-
 import os
 import multiprocessing.connection
 import sys
diff --git a/tools/commissioner_thci/example_send_mlr.py b/tools/commissioner_thci/example_send_mlr.py
index 938473ac..3c9e8ffd 100644
--- a/tools/commissioner_thci/example_send_mlr.py
+++ b/tools/commissioner_thci/example_send_mlr.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 #   Copyright (c) 2019, The OpenThread Commissioner Authors.
@@ -71,8 +71,8 @@ def test_mlr():
         comm.start(BORDER_AGENT_ADDR, BORDER_AGENT_PORT)
         assert comm.isActive()
 
-        print("commissioner connected, session ID = {}".format(
-            comm.getSessionId()))
+        print(("commissioner connected, session ID = {}".format(
+            comm.getSessionId())))
 
         ## Send MLR.req
         comm.MLR([MA1, MA2], 60)