ABSTRACT Background and aim: It is well established that the rate of gastric lesions increases in diabetic rats. Recently, the protective effect of hydrogen sulfide (H2S) in gastric mucosa has been proven. This study aimed to determine the release of H2S and mRNA expression of cystathionine gamma lyase (CSE) in gastric mucosa in alloxan-diabetic rats in response to distention-induced gastric acid secretion. Twenty-four rats were randomly assigned to 4 groups (6 in each). They were the normal-control, distention-control, diabetic-control, and distention-diabetic groups. Under anesthesia, animals underwent a tracheotomy and midline laparotomy. To washout the gastric contents, a catheter was inserted in the stomach through the duodenum. To determine the effect of distention-induced gastric acid secretion on H2S release and mRNA expression of CSE, the stomachs were distended by normal saline. At the end of experiments, animals were sacrificed and the gastric mucosa was collected to determine H2S concentration and to quantify mRNA expression of CSE by quantitative real-time PCR. Mucosal release of H2S and mRNA expression of CSE significantly increased in response to stimulated gastric acid secretion in normal rats (P<0.01), while the increases in diabetic rats were not significant. Basal release of H2S and mRNA expression of CSE in gastric mucosa were significantly in diabetic rats lower than normal rats. On the basis of the results, we conclude that the decreased release of H2S in response to basal and stimulated gastric acid output in alloxan-diabetic rats compared to normal rats is largely due to downregulation of mRNA expression of CSE.