A series of 8H-indeno[1,2-d]thiazoles containing various N-substituted amino groups at the 2 position were synthesized by the reaction of 2-bromo-indanones and N-substituted thioureas. Their anti-ulcerous activity was evaluated. Alkylamino derivatives have a more potent inhibitory behavior on ethanol-induced gastric ulcers compared with arylamino derivatives. We also studied the effect of various substituents on the both benzene and pyridine ring of 2-pyridylamino derivatives on ethanol-induced gastric ulcers. However no clear effects were observed. Among 3-morpholinopropylamino derivatives, 5-isopropyl- (21) and 7-chloro-2-(3-morpholinopropyl)amino-8H-indeno[1,2-d]thiazole (25) showed a considerably stronger inhibitory behavior on hydrochloric acid-induced gastric ulcers than cetraxate hydrochloride. Furthermore, 3-morpholinopropylamino derivatives have potent inhibitory effects on gastric acid secretion in pylorus ligated rats.