Objective  This experiment was designed to test the changes in the malonyldialdehyde(MDA) content and the activities of catalase (CAT) and Ca    2+    ATPase in rat gastric mucosa under stress.Methods  The animal  model was established by soaking the rat in water after binding four limbs and fixing the head on shelf.The level of MDA and the activities CAT and Ca    2+    ATPase in rat gastric mucosa were determined. Results  The content of MDA was increased with the duration of stress and the activities of CAT and Ca    2+    ATPase were enhanced compensatively.The peak was found at the second hour after stress.Conclusion  The radials increased as stress time went on.Although the activities of radical  clearing system enhanced compa~ratively,it could not clear the increasing radicals timely.Thus the injury of rat gastric mucosa occurred.