diff --git a/CHANGELOG.md b/CHANGELOG.md
index a31a583..d77ae73 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
 
+### Deprecated
+- Support for Python 3.4 and 3.5 ([#503](https://github.com/pdfminer/pdfminer.six/pull/503))
+
 ### Added
 
 - Option to disable boxes flow layout analysis when using pdf2txt ([#479](https://github.com/pdfminer/pdfminer.six/pull/479))
diff --git a/README.md b/README.md
index e2552a6..c78565a 100644
--- a/README.md
+++ b/README.md
@@ -38,7 +38,7 @@ Features
 How to use
 ----------
 
- * Install Python 3.4 or newer
+ * Install Python 3.6 or newer (3.4 and 3.5 are deprecated)
  * Install
 
     `pip install pdfminer.six`
diff --git a/docs/source/index.rst b/docs/source/index.rst
index e5d19a7..dd06e2d 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -57,7 +57,7 @@ Features
 Installation instructions
 =========================
 
-Before using it, you must install it using Python 3.4 or newer.
+Before using it, you must install it using Python 3.6 or newer (3.4 and 3.5 are deprecated).
 
 ::
 
diff --git a/pdfminer/__init__.py b/pdfminer/__init__.py
index 109a3c6..744a1c9 100644
--- a/pdfminer/__init__.py
+++ b/pdfminer/__init__.py
@@ -1,4 +1,12 @@
+import sys
+import warnings
+
+
 __version__ = '20200726'
 
+if sys.version_info < (3, 6):
+    warnings.warn('Python 3.4 and 3.5 are deprecated. '
+                  'Please upgrade to Python 3.6 or newer.')
+
 if __name__ == '__main__':
     print(__version__)