diff --git a/.travis.yml b/.travis.yml
index 4b42639..762448b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -13,6 +13,10 @@ before_install:
   - cd kytea-0.4.7 && ./configure && sudo make && sudo make install && cd ..
   - sudo ldconfig -v
 
+env:
+  - 
+  - BUILD_WORD_TOKENIZER=0
+
 install:
   - pip install .
 
@@ -20,4 +24,4 @@ python:
       - 3.6
 
 script:
-      - nosetests tests
+      - python -m pytest
diff --git a/README.md b/README.md
index f821fff..74b5ea5 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,10 @@ tiny_tokenizer requires following libraries.
 You can install tiny_tokenizer via pip.
 `pip install tiny_tokenizer`
 
+Or, you can install tiny_tokenizer only with SentenceTokenizer by the following command.
+`BUILD_WORD_TOKENIZER=0 pip install tiny_tokenizer`
+
+
 ### Quick start: Docker
 
 You can use tiny_tokenizer using the Docker container.
@@ -30,6 +34,7 @@ docker build -t himkt/tiny_tokenizer .
 docker run -it himkt/tiny_tokenizer
 ```
 
+
 ### Example
 
 `python3 example/tokenize_document.py`
@@ -54,10 +59,11 @@ Tokenizer (Sentencepiece): ▁ 名前 はまだ ない
 Tokenizer (Character): 名 前 は ま だ な い
 ```
 
+
 ### Test
 
 ```
-nosetests
+python -m pytest
 ```
 
 ### Acknowledgement
diff --git a/setup.py b/setup.py
index 08b5f39..814647d 100644
--- a/setup.py
+++ b/setup.py
@@ -4,12 +4,29 @@
 from setuptools import find_packages
 from setuptools import setup
 
+from os import getenv
 
-setup(name='tiny_tokenizer',
-      version='1.3.0',
-      description='Tiny Word/Sentence Tokenizer',
-      author='himkt',
-      author_email='himkt@klis.tsukuba.ac.jp',
-      install_requires=['natto-py', 'kytea', 'sentencepiece'],
-      url='https://github.com/himkt/tiny_tokenizer',
-      packages=find_packages())
+
+try:
+    BUILD_WORD_TOKENIZER = int(getenv('BUILD_WORD_TOKENIZER', 1))
+except:
+    raise ValueError('BUILD_WORD_TOKENIZER should be integer')
+
+
+install_requires = []
+if BUILD_WORD_TOKENIZER == 1:
+    install_requires.extend(['natto-py', 'kytea', 'sentencepiece'])
+else:
+    print('Install sentence tokenizer only')
+
+
+setup(
+    name='tiny_tokenizer',
+    version='1.3.1',
+    description='Tiny Word/Sentence Tokenizer',
+    author='himkt',
+    author_email='himkt@klis.tsukuba.ac.jp',
+    install_requires=install_requires,
+    url='https://github.com/himkt/tiny_tokenizer',
+    packages=find_packages()
+)
diff --git a/tests/test_word_tokenize.py b/tests/test_word_tokenize.py
index fc369ce..bb1e8fb 100644
--- a/tests/test_word_tokenize.py
+++ b/tests/test_word_tokenize.py
@@ -1,5 +1,7 @@
 from tiny_tokenizer.word_tokenizer import WordTokenizer
+
 import unittest
+import pytest
 
 
 SENTENCE1 = '吾輩は猫である'
@@ -10,21 +12,33 @@ class WordTokenizerTest(unittest.TestCase):
 
     def test_word_tokenize_with_kytea(self):
         """Test KyTea tokenizer."""
-        tokenizer = WordTokenizer('KyTea')
+        try:
+            tokenizer = WordTokenizer('KyTea')
+        except ModuleNotFoundError:
+            pytest.skip('skip kytea')
+
         expect = '吾輩 は 猫 で あ る'.split(' ')
         result = tokenizer.tokenize(SENTENCE1)
         self.assertEqual(expect, result)
 
     def test_word_tokenize_with_mecab(self):
         """Test MeCab tokenizer."""
-        tokenizer = WordTokenizer('MeCab')
+        try:
+            tokenizer = WordTokenizer('MeCab')
+        except ModuleNotFoundError:
+            pytest.skip('skip mecab')
+
         expect = '吾輩 は 猫 で ある'.split(' ')
         result = tokenizer.tokenize(SENTENCE1)
         self.assertEqual(expect, result)
 
     def test_word_tokenize_with_sentencepiece(self):
         """Test Sentencepiece tokenizer."""
-        tokenizer = WordTokenizer('Sentencepiece', 'data/model.spm')
+        try:
+            tokenizer = WordTokenizer('Sentencepiece', 'data/model.spm')
+        except ModuleNotFoundError:
+            pytest.skip('skip sentencepiece')
+
         expect = '▁ 吾 輩 は 猫 である'.split(' ')
         result = tokenizer.tokenize(SENTENCE1)
         self.assertEqual(expect, result)
@@ -49,21 +63,33 @@ class WordTokenizerWithLowerCaseTest(unittest.TestCase):
 
     def test_word_tokenize_with_kytea(self):
         """Test KyTea tokenizer."""
-        tokenizer = WordTokenizer('kytea')
+        try:
+            tokenizer = WordTokenizer('kytea')
+        except ModuleNotFoundError:
+            pytest.skip('skip kytea')
+
         expect = '吾輩 は 猫 で あ る'.split(' ')
         result = tokenizer.tokenize(SENTENCE1)
         self.assertEqual(expect, result)
 
     def test_word_tokenize_with_mecab(self):
         """Test MeCab tokenizer."""
-        tokenizer = WordTokenizer('mecab')
+        try:
+            tokenizer = WordTokenizer('mecab')
+        except ModuleNotFoundError:
+            pytest.skip('skip mecab')
+
         expect = '吾輩 は 猫 で ある'.split(' ')
         result = tokenizer.tokenize(SENTENCE1)
         self.assertEqual(expect, result)
 
     def test_word_tokenize_with_sentencepiece(self):
         """Test Sentencepiece tokenizer."""
-        tokenizer = WordTokenizer('sentencepiece', 'data/model.spm')
+        try:
+            tokenizer = WordTokenizer('Sentencepiece', 'data/model.spm')
+        except ModuleNotFoundError:
+            pytest.skip('skip sentencepiece')
+
         expect = '▁ 吾 輩 は 猫 である'.split(' ')
         result = tokenizer.tokenize(SENTENCE1)
         self.assertEqual(expect, result)
diff --git a/tiny_tokenizer/__init__.py b/tiny_tokenizer/__init__.py
index c68b554..a932ffc 100644
--- a/tiny_tokenizer/__init__.py
+++ b/tiny_tokenizer/__init__.py
@@ -1,4 +1,4 @@
 from .sentence_tokenizer import SentenceTokenizer
 from .word_tokenizer import WordTokenizer
 
-__version__ = '1.3.0'
+__version__ = "1.3.1"
diff --git a/tiny_tokenizer/word_tokenizer.py b/tiny_tokenizer/word_tokenizer.py
index 360e174..dedab21 100644
--- a/tiny_tokenizer/word_tokenizer.py
+++ b/tiny_tokenizer/word_tokenizer.py
@@ -27,20 +27,33 @@ def __init__(self, tokenizer=None, flags=''):
 
         # use external libraries
         if __tokenizer == 'mecab':
-            import natto
+            try:
+                import natto
+            except ModuleNotFoundError:
+                raise ModuleNotFoundError('natto-py is not installed')
+                exit()
+
             flags = '-Owakati' if not flags else flags
             self.__tokenizer = natto.MeCab(flags)
             self.__tokenizer_name = 'MeCab'
             self.tokenize = self.__mecab_tokenize
 
         if __tokenizer == 'kytea':
-            import Mykytea
+            try:
+                import Mykytea
+            except ModuleNotFoundError:
+                raise ModuleNotFoundError('kytea is not installed')
+
             self.__tokenizer = Mykytea.Mykytea(flags)
             self.__tokenizer_name = 'KyTea'
             self.tokenize = self.__kytea_tokenize
 
         elif __tokenizer == 'sentencepiece':
-            import sentencepiece
+            try:
+                import sentencepiece
+            except ModuleNotFoundError:
+                raise ModuleNotFoundError('sentencepiece is not installed')
+
             self.__tokenizer = sentencepiece.SentencePieceProcessor()
             self.__tokenizer.load(flags)
             self.__tokenizer_name = 'Sentencepiece'