diff --git a/rosserial_python/src/rosserial_python/SerialClient.py b/rosserial_python/src/rosserial_python/SerialClient.py
index b9e5b6c77..59afc9bf9 100644
--- a/rosserial_python/src/rosserial_python/SerialClient.py
+++ b/rosserial_python/src/rosserial_python/SerialClient.py
@@ -39,13 +39,13 @@
 import threading
 import sys
 import multiprocessing
-import StringIO
+import io
 import errno
 import signal
 import socket
 import struct
 import time
-from Queue import Queue
+from queue import Queue
 
 from serial import Serial, SerialException, SerialTimeoutException
 
@@ -132,7 +132,7 @@ def __init__(self, topic_info, parent):
 
     def callback(self, msg):
         """ Forward message to serial device. """
-        data_buffer = StringIO.StringIO()
+        data_buffer = io.BytesIO()
         msg.serialize(data_buffer)
         self.parent.send(self.id, data_buffer.getvalue())
 
@@ -167,7 +167,7 @@ def unregister(self):
 
     def callback(self, req):
         """ Forward request to serial device. """
-        data_buffer = StringIO.StringIO()
+        data_buffer = io.BytesIO()
         req.serialize(data_buffer)
         self.response = None
         if self.parent.send(self.id, data_buffer.getvalue()) >= 0:
@@ -209,7 +209,7 @@ def handlePacket(self, data):
         # call service proxy
         resp = self.proxy(req)
         # serialize and publish
-        data_buffer = StringIO.StringIO()
+        data_buffer = io.BytesIO()
         resp.serialize(data_buffer)
         self.parent.send(self.id, data_buffer.getvalue())
 
@@ -368,8 +368,8 @@ def __init__(self, port=None, baud=57600, timeout=5.0, fix_pyserial_for_test=Fal
 
         # hydro introduces protocol ver2 which must match node_handle.h
         # The protocol version is sent as the 2nd sync byte emitted by each end
-        self.protocol_ver1 = '\xff'
-        self.protocol_ver2 = '\xfe'
+        self.protocol_ver1 = b'\xff'
+        self.protocol_ver2 = b'\xfe'
         self.protocol_ver = self.protocol_ver2
 
         self.publishers = dict()  # id:Publishers
@@ -409,7 +409,7 @@ def requestTopics(self):
                 self.port.flushInput()
 
         # request topic sync
-        self.write_queue.put("\xff" + self.protocol_ver + "\x00\x00\xff\x00\x00\xff")
+        self.write_queue.put(b"\xff" + self.protocol_ver + b"\x00\x00\xff\x00\x00\xff")
 
     def txStopRequest(self, signal, frame):
         """ send stop tx request to arduino when receive SIGINT(Ctrl-c)"""
@@ -417,7 +417,7 @@ def txStopRequest(self, signal, frame):
             with self.read_lock:
                 self.port.flushInput()
 
-        self.write_queue.put("\xff" + self.protocol_ver + "\x00\x00\xff\x0b\x00\xf4")
+        self.write_queue.put(b"\xff" + self.protocol_ver + b"\x00\x00\xff\x0b\x00\xf4")
 
         # tx_stop_request is x0b
         rospy.loginfo("Send tx stop request")
@@ -479,7 +479,7 @@ def run(self):
                 flag = [0, 0]
                 read_step = 'syncflag'
                 flag[0] = self.tryRead(1)
-                if (flag[0] != '\xff'):
+                if (flag[0] != b'\xff'):
                     continue
 
                 # Find protocol version.
@@ -488,7 +488,7 @@ def run(self):
                 if flag[1] != self.protocol_ver:
                     self.sendDiagnostics(diagnostic_msgs.msg.DiagnosticStatus.ERROR, ERROR_MISMATCHED_PROTOCOL)
                     rospy.logerr("Mismatched protocol version in packet (%s): lost sync or rosserial_python is from different ros release than the rosserial client" % repr(flag[1]))
-                    protocol_ver_msgs = {'\xff': 'Rev 0 (rosserial 0.4 and earlier)', '\xfe': 'Rev 1 (rosserial 0.5+)', '\xfd': 'Some future rosserial version'}
+                    protocol_ver_msgs = {b'\xff': 'Rev 0 (rosserial 0.4 and earlier)', b'\xfe': 'Rev 1 (rosserial 0.5+)', b'\xfd': 'Some future rosserial version'}
                     if flag[1] in protocol_ver_msgs:
                         found_ver_msg = 'Protocol version of client is ' + protocol_ver_msgs[flag[1]]
                     else:
@@ -499,23 +499,24 @@ def run(self):
                 # Read message length.
                 read_step = 'message length'
                 msg_len_bytes = self.tryRead(2)
-                msg_length, = struct.unpack("<h", msg_len_bytes)
+                msg_length, = struct.unpack("<H", msg_len_bytes)
 
                 # Read message length checksum.
                 read_step = 'message length checksum'
-                msg_len_chk = self.tryRead(1)
-                msg_len_checksum = sum(map(ord, msg_len_bytes)) + ord(msg_len_chk)
+                msg_len_chk_bytes = self.tryRead(1)
+                msg_len_chk, = struct.unpack("<B", msg_len_chk_bytes)
+                msg_len_checksum = sum(msg_len_bytes) + msg_len_chk
 
                 # Validate message length checksum.
                 if msg_len_checksum % 256 != 255:
                     rospy.loginfo("wrong checksum for msg length, length %d" %(msg_length))
-                    rospy.loginfo("chk is %d" % ord(msg_len_chk))
+                    rospy.loginfo("chk is %d" % msg_len_chk)
                     continue
 
                 # Read topic id (2 bytes)
                 read_step = 'topic id'
                 topic_id_header = self.tryRead(2)
-                topic_id, = struct.unpack("<h", topic_id_header)
+                topic_id, = struct.unpack("<H", topic_id_header)
 
                 # Read serialized message data.
                 read_step = 'data'
@@ -529,8 +530,9 @@ def run(self):
 
                 # Reada checksum for topic id and msg
                 read_step = 'data checksum'
-                chk = self.tryRead(1)
-                checksum = sum(map(ord, topic_id_header) ) + sum(map(ord, msg)) + ord(chk)
+                chk_bytes = self.tryRead(1)
+                chk, = struct.unpack("<B", chk_bytes)
+                checksum = sum(topic_id_header) + sum(msg) + chk
 
                 # Validate checksum.
                 if checksum % 256 == 255:
@@ -679,7 +681,7 @@ def handleTimeRequest(self, data):
         """ Respond to device with system time. """
         t = Time()
         t.data = rospy.Time.now()
-        data_buffer = StringIO.StringIO()
+        data_buffer = io.BytesIO()
         t.serialize(data_buffer)
         self.send( TopicInfo.ID_TIME, data_buffer.getvalue() )
         self.lastsync = rospy.Time.now()
@@ -716,7 +718,7 @@ def handleParameterRequest(self, data):
             resp.floats =param
         if t == str:
             resp.strings = param
-        data_buffer = StringIO.StringIO()
+        data_buffer = io.BytesIO()
         resp.serialize(data_buffer)
         self.send(TopicInfo.ID_PARAMETER_REQUEST, data_buffer.getvalue())
 
@@ -761,9 +763,9 @@ def _send(self, topic, msg):
             #modified frame : header(2 bytes) + msg_len(2 bytes) + msg_len_chk(1 byte) + topic_id(2 bytes) + msg(x bytes) + msg_topic_id_chk(1 byte)
             # second byte of header is protocol version
             msg_len_checksum = 255 - ( ((length&255) + (length>>8))%256 )
-            msg_checksum = 255 - ( ((topic&255) + (topic>>8) + sum([ord(x) for x in msg]))%256 )
-            data = "\xff" + self.protocol_ver  + chr(length&255) + chr(length>>8) + chr(msg_len_checksum) + chr(topic&255) + chr(topic>>8)
-            data = data + msg + chr(msg_checksum)
+            msg_checksum = 255 - ( ((topic&255) + (topic>>8) + sum(msg))%256 )
+            data = b"\xff" + self.protocol_ver  + struct.pack("<BBBBB", length&255, length>>8, msg_len_checksum, topic&255, topic>>8)
+            data = data + msg + struct.pack("<B", msg_checksum)
             self._write(data)
             return length
 
@@ -781,7 +783,7 @@ def processWriteQueue(self):
                         if isinstance(data, tuple):
                             topic, msg = data
                             self._send(topic, msg)
-                        elif isinstance(data, basestring):
+                        elif isinstance(data, bytes):
                             self._write(data)
                         else:
                             rospy.logerr("Trying to write invalid data type: %s" % type(data))
diff --git a/rosserial_python/src/rosserial_python/__init__.py b/rosserial_python/src/rosserial_python/__init__.py
index 2146287ff..8e9ada624 100644
--- a/rosserial_python/src/rosserial_python/__init__.py
+++ b/rosserial_python/src/rosserial_python/__init__.py
@@ -1 +1 @@
-from SerialClient import *
+from rosserial_python.SerialClient import *