Background. Gastrointestinal complaints are common among diabetic patients. The gastrointestinal tract contains melatonin. The binding sites of melatonin have been identified in all GIT tissues. Melatonin can modify activities of the gut and liver. The aim of this study was to evaluate the possible protective effects of melatonin against gastric motility and secretary responses in Streptozotocin-induced diabetes in rats. Methods. Streptozotocin was injected intraperitoneally at a single dose of 60 mg/kg for diabetes induction. One week after inducing diabetes, Melatonin (5, 10, 20 mg/kg/day, IP.) was injected for 14 days. Gastric acid and mucus were measured in all animals by chemical methods. Gastric motility was investigated by powerlab system. Results. Streptozotocin induced a significant increase in blood glucose levels (p<0.001) and significant decrease in gastric acid, mucus, motility and body weight in diabetic groups. Treatment of diabetic rats with melatonin significantly reduced blood glucose (p<0.001) and increased gastric mucus (p<0.001) and motility (p<0.01 and p<0.05 in groups 4 and 5 respectively) with no effect on body weight and gastric acid concentration. Conclusion. These data suggested that melatonin treatment has a therapeutic effect on diabetic gastrointestinal disturbances by reduction of serum glucose and increasing gastric motility and gastric mucus levels, but no effect on gastric acid and body weight. © 2015, Acta Endocrinologica Foundation. All rights reserved.