diff --git a/requirements.txt b/requirements.txt
index 63a9655..e69de29 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1 +0,0 @@
-six>=1.13.0
\ No newline at end of file
diff --git a/setup.py b/setup.py
index 9331bec..178ec9b 100644
--- a/setup.py
+++ b/setup.py
@@ -14,7 +14,7 @@
     license="Apache License, Version 2.0",
     packages=["treelib"],
     keywords=["data structure", "tree", "tools"],
-    install_requires=["six"],
+    install_requires=[],
     classifiers=[
         "Development Status :: 5 - Production/Stable",
         "Environment :: Console",
diff --git a/treelib/__init__.py b/treelib/__init__.py
index 4902412..677c57d 100644
--- a/treelib/__init__.py
+++ b/treelib/__init__.py
@@ -17,22 +17,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 """
-treelib - Python 2/3 Tree Implementation
+treelib - Python Tree Implementation
 
 `treelib` is a Python module with two primary classes: Node and Tree.
 Tree is a self-contained structure with some nodes and connected by branches.
 A tree owns merely a root, while a node (except root) has some children and one parent.
-
-Note: To solve string compatibility between Python 2.x and 3.x, treelib follows
-the way of porting Python 3.x to 2/3. That means, all strings are manipulated as
-unicode and you do not need u'' prefix anymore. The impacted functions include `str()`,
-`show()` and `save2file()` routines.
-But if your data contains non-ascii characters and Python 2.x is used,
-you have to trigger the compatibility by declaring `unicode_literals` in the code:
-
-.. code-block:: python
-
-   >>> from __future__ import unicode_literals
 """
 
 from .tree import Tree  # noqa: F401
diff --git a/treelib/node.py b/treelib/node.py
index 958c734..c069e76 100644
--- a/treelib/node.py
+++ b/treelib/node.py
@@ -23,8 +23,6 @@
 A :class:`Node` object contains basic properties such as node identifier,
 node tag, parent node, children nodes etc., and some operations for a node.
 """
-from __future__ import unicode_literals
-
 import copy
 import uuid
 from collections import defaultdict
@@ -34,7 +32,7 @@
 from .misc import deprecated
 
 
-class Node(object):
+class Node:
     """
     Nodes are elementary objects that are stored in the `_nodes` dictionary of a Tree.
     Use `data` attribute to store node-specific data.
diff --git a/treelib/tree.py b/treelib/tree.py
index 1cc9ac8..cbd4d12 100644
--- a/treelib/tree.py
+++ b/treelib/tree.py
@@ -26,24 +26,11 @@
 When deep=True, a deepcopy operation is performed on feeding tree parameter and more memory
 is required to create the tree.
 """
-from __future__ import print_function
-from __future__ import unicode_literals
-
-try:
-    from builtins import str as text
-except ImportError:
-    from __builtin__ import str as text
-
 import codecs
 import json
 import uuid
 from copy import deepcopy
-from six import python_2_unicode_compatible, iteritems
-
-try:
-    from StringIO import StringIO
-except ImportError:
-    from io import StringIO
+from io import StringIO
 
 from .exceptions import (
     NodeIDAbsentError,
@@ -58,8 +45,7 @@
 __author__ = "chenxm"
 
 
-@python_2_unicode_compatible
-class Tree(object):
+class Tree:
     """Tree objects are made of Node(s) stored in _nodes dictionary."""
 
     #: ROOT, DEPTH, WIDTH, ZIGZAG constants :
@@ -89,7 +75,7 @@ def __init__(self, tree=None, deep=False, node_class=None, identifier=None):
 
         if tree is not None:
             self.root = tree.root
-            for nid, node in iteritems(tree.nodes):
+            for nid, node in tree.nodes.items():
                 new_node = deepcopy(node) if deep else node
                 self._nodes[nid] = new_node
                 if tree.identifier != self._identifier:
@@ -687,9 +673,9 @@ def paste(self, nid, new_tree, deep=False):
 
         set_joint = set(new_tree._nodes) & set(self._nodes)  # joint keys
         if set_joint:
-            raise ValueError("Duplicated nodes %s exists." % list(map(text, set_joint)))
+            raise ValueError("Duplicated nodes %s exists." % list(map(str, set_joint)))
 
-        for cid, node in iteritems(new_tree.nodes):
+        for cid, node in new_tree.nodes.items():
             if deep:
                 node = deepcopy(new_tree[node])
             self._nodes.update({cid: node})
@@ -1017,7 +1003,7 @@ def update_node(self, nid, **attrs):
         :return: None
         """
         cn = self[nid]
-        for attr, val in iteritems(attrs):
+        for attr, val in attrs.items():
             if attr == "identifier":
                 # Updating node id meets following contraints:
                 # * Update node identifier property