diff --git a/doc/source/whatsnew/v1.1.0.rst b/doc/source/whatsnew/v1.1.0.rst
index 798a3d838ef7e..3976696ecdd06 100644
--- a/doc/source/whatsnew/v1.1.0.rst
+++ b/doc/source/whatsnew/v1.1.0.rst
@@ -1053,6 +1053,7 @@ I/O
 - Bug in :meth:`~HDFStore.create_table` now raises an error when `column` argument was not specified in `data_columns` on input (:issue:`28156`)
 - :meth:`read_json` now could read line-delimited json file from a file url while `lines` and `chunksize` are set.
 - Bug in :meth:`DataFrame.to_sql` when reading DataFrames with ``-np.inf`` entries with MySQL now has a more explicit ``ValueError`` (:issue:`34431`)
+- Bug where capitalised files extensions were not decompressed by read_* functions (:issue:`35164`)
 - Bug in :meth:`read_excel` that was raising a ``TypeError`` when ``header=None`` and ``index_col`` given as list (:issue:`31783`)
 - Bug in "meth"`read_excel` where datetime values are used in the header in a `MultiIndex` (:issue:`34748`)
 
diff --git a/pandas/io/common.py b/pandas/io/common.py
index 51323c5ff3ef5..4e6395fc67b2a 100644
--- a/pandas/io/common.py
+++ b/pandas/io/common.py
@@ -311,7 +311,7 @@ def infer_compression(
 
         # Infer compression from the filename/URL extension
         for compression, extension in _compression_to_extension.items():
-            if filepath_or_buffer.endswith(extension):
+            if filepath_or_buffer.lower().endswith(extension):
                 return compression
         return None
 
diff --git a/pandas/tests/io/test_common.py b/pandas/tests/io/test_common.py
index e2f4ae04c1f9f..dde38eb55ea7f 100644
--- a/pandas/tests/io/test_common.py
+++ b/pandas/tests/io/test_common.py
@@ -87,7 +87,17 @@ def test_stringify_path_fspath(self):
 
     @pytest.mark.parametrize(
         "extension,expected",
-        [("", None), (".gz", "gzip"), (".bz2", "bz2"), (".zip", "zip"), (".xz", "xz")],
+        [
+            ("", None),
+            (".gz", "gzip"),
+            (".bz2", "bz2"),
+            (".zip", "zip"),
+            (".xz", "xz"),
+            (".GZ", "gzip"),
+            (".BZ2", "bz2"),
+            (".ZIP", "zip"),
+            (".XZ", "xz"),
+        ],
     )
     @pytest.mark.parametrize("path_type", path_types)
     def test_infer_compression_from_path(self, extension, expected, path_type):