Trichosanthes cucumerina Linn. (cucurbitaceae) is widely used in Indian folk medicine for variety of disease conditions. The aim of present study was to evaluate the antiulcer activity of 50% ethanolic extract of fruits of Trichosanthes cucumerina Linn. (TCFE) using various experimental models of gastric and duodenal ulceration in rats. Oral administration of 50% ethanolic extract of fruits of Trichosanthes cucumerina Linn. was evaluated in rats against ethanol, aspirin and pylorus ligated gastric ulcers as well as cysteamine-induced duodenal ulcers. In all the models studied, the antiulcer activity of TCFE compared with that of cimetidine (100 mg/kg, p.o.), an $H_2$ receptor antagonist. TCFE showed significant antiulcer activity in ethanol-induced and aspirin-induced gastric ulcer models. In 19 h pylorus ligated rats, significant reduction in ulcer index, total acidity and pepsin activity was observed with TCFE, when compared with the control group. Mucosal defensive factors such as pH, mucin activity and gastric wall mucous content was found to be increased with TCFE. TCFE was also, afforded remarkable protection in cysteamine-induced duodenal lesions. The antiulcer activity of TCFE was comparable with that of cimetidine. Thus, TCFE possess significant antiulcer activity against both gastric and duodenal ulcers in rats. The antiulcer activity may be attributed to its cytoprotective action and inhibition of acid secretary parameters.