diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index f14ec10e3..8a7b03d17 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -4,6 +4,9 @@ Jupytext ChangeLog
 1.10.1 (2021-02-??)
 -------------------
 
+**Added**
+- Sage notebooks are supported. They can be converted to `.sage` and `.md` files and back. Thanks to Lars Franke for suggesting this! ([#727](https://github.com/mwouts/jupytext/issues/727))
+
 
 1.10.0 (2021-02-04)
 -------------------
diff --git a/docs/languages.md b/docs/languages.md
index 859ef5178..7efd87a67 100644
--- a/docs/languages.md
+++ b/docs/languages.md
@@ -21,6 +21,7 @@ Jupytext works with notebooks in any of the following languages:
 - R
 - Robot Framework
 - Rust/Evxcr
+- Sage
 - Scala
 - Scheme
 - Script of Script
diff --git a/jupytext/formats.py b/jupytext/formats.py
index 4346e4384..23425b876 100644
--- a/jupytext/formats.py
+++ b/jupytext/formats.py
@@ -766,6 +766,11 @@ def auto_ext_from_metadata(metadata):
     """Script extension from notebook metadata"""
     auto_ext = metadata.get("language_info", {}).get("file_extension")
 
+    # Sage notebooks have ".py" as the associated extension in "language_info",
+    # so we change it to ".sage" in that case, see #727
+    if auto_ext == ".py" and metadata.get("kernelspec", {}).get("language") == "sage":
+        auto_ext = ".sage"
+
     if auto_ext is None:
         language = metadata.get("kernelspec", {}).get("language") or metadata.get(
             "jupytext", {}
diff --git a/jupytext/languages.py b/jupytext/languages.py
index b52bbe47d..284c3ba0f 100644
--- a/jupytext/languages.py
+++ b/jupytext/languages.py
@@ -57,6 +57,7 @@
     ".sos": {"language": "sos", "comment": "#"},
     ".java": {"language": "java", "comment": "//"},
     ".groovy": {"language": "groovy", "comment": "//"},
+    ".sage": {"language": "sage", "comment": "#"},
 }
 
 _COMMENT_CHARS = [
diff --git a/tests/notebooks/ipynb_sage/sage_print_hello.ipynb b/tests/notebooks/ipynb_sage/sage_print_hello.ipynb
new file mode 100644
index 000000000..c1206f2a2
--- /dev/null
+++ b/tests/notebooks/ipynb_sage/sage_print_hello.ipynb
@@ -0,0 +1,34 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print(\"Hello world\")"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "SageMath 9.2",
+   "language": "sage",
+   "name": "sagemath"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.9.1"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}
diff --git a/tests/notebooks/mirror/ipynb_to_Rmd/sage_print_hello.Rmd b/tests/notebooks/mirror/ipynb_to_Rmd/sage_print_hello.Rmd
new file mode 100644
index 000000000..6793b5c45
--- /dev/null
+++ b/tests/notebooks/mirror/ipynb_to_Rmd/sage_print_hello.Rmd
@@ -0,0 +1,11 @@
+---
+jupyter:
+  kernelspec:
+    display_name: SageMath 9.2
+    language: sage
+    name: sagemath
+---
+
+```{sage}
+print("Hello world")
+```
diff --git a/tests/notebooks/mirror/ipynb_to_hydrogen/sage_print_hello.sage b/tests/notebooks/mirror/ipynb_to_hydrogen/sage_print_hello.sage
new file mode 100644
index 000000000..bf0bfccb9
--- /dev/null
+++ b/tests/notebooks/mirror/ipynb_to_hydrogen/sage_print_hello.sage
@@ -0,0 +1,10 @@
+# ---
+# jupyter:
+#   kernelspec:
+#     display_name: SageMath 9.2
+#     language: sage
+#     name: sagemath
+# ---
+
+# %%
+print("Hello world")
diff --git a/tests/notebooks/mirror/ipynb_to_md/sage_print_hello.md b/tests/notebooks/mirror/ipynb_to_md/sage_print_hello.md
new file mode 100644
index 000000000..6131043b8
--- /dev/null
+++ b/tests/notebooks/mirror/ipynb_to_md/sage_print_hello.md
@@ -0,0 +1,11 @@
+---
+jupyter:
+  kernelspec:
+    display_name: SageMath 9.2
+    language: sage
+    name: sagemath
+---
+
+```sage
+print("Hello world")
+```
diff --git a/tests/notebooks/mirror/ipynb_to_myst/sage_print_hello.md b/tests/notebooks/mirror/ipynb_to_myst/sage_print_hello.md
new file mode 100644
index 000000000..445c3ee86
--- /dev/null
+++ b/tests/notebooks/mirror/ipynb_to_myst/sage_print_hello.md
@@ -0,0 +1,10 @@
+---
+kernelspec:
+  display_name: SageMath 9.2
+  language: sage
+  name: sagemath
+---
+
+```{code-cell} ipython3
+print("Hello world")
+```
diff --git a/tests/notebooks/mirror/ipynb_to_percent/sage_print_hello.sage b/tests/notebooks/mirror/ipynb_to_percent/sage_print_hello.sage
new file mode 100644
index 000000000..bf0bfccb9
--- /dev/null
+++ b/tests/notebooks/mirror/ipynb_to_percent/sage_print_hello.sage
@@ -0,0 +1,10 @@
+# ---
+# jupyter:
+#   kernelspec:
+#     display_name: SageMath 9.2
+#     language: sage
+#     name: sagemath
+# ---
+
+# %%
+print("Hello world")
diff --git a/tests/notebooks/mirror/ipynb_to_script/sage_print_hello.sage b/tests/notebooks/mirror/ipynb_to_script/sage_print_hello.sage
new file mode 100644
index 000000000..09e3f421d
--- /dev/null
+++ b/tests/notebooks/mirror/ipynb_to_script/sage_print_hello.sage
@@ -0,0 +1,9 @@
+# ---
+# jupyter:
+#   kernelspec:
+#     display_name: SageMath 9.2
+#     language: sage
+#     name: sagemath
+# ---
+
+print("Hello world")
diff --git a/tests/test_auto_ext.py b/tests/test_auto_ext.py
index 721ba2ae1..d68fb6686 100644
--- a/tests/test_auto_ext.py
+++ b/tests/test_auto_ext.py
@@ -39,6 +39,10 @@ def test_auto_from_kernelspecs_works(nb_file):
     elif expected_ext == ".fs":
         expected_ext = ".fsx"
     auto_ext = auto_ext_from_metadata(nb.metadata)
+    if auto_ext == ".sage":
+        pytest.xfail(
+            "Sage notebooks have Python in their language_info metadata, see #727"
+        )
     assert auto_ext == expected_ext