diff --git a/tools/workspace/os.bzl b/tools/workspace/os.bzl
index a37364a83294..d33b972419e6 100644
--- a/tools/workspace/os.bzl
+++ b/tools/workspace/os.bzl
@@ -109,7 +109,12 @@ def _determine_macos(repository_ctx):
     macos_release = ".".join(major_minor_versions)
 
     # Match supported macOS release(s).
-    if macos_release in ["10.15"]:
+    if macos_release in ["10.15", "11.0"]:
+        if macos_release == "11.0":
+            print(
+                "WARNING: macOS Big Sur 11.0 is NOT yet supported. " +
+                "Compilation, tests, and/or other functionality may fail.",
+            )
         return _make_result(macos_release = macos_release)
 
     # Nothing matched.