2, 4-Diamino-[E]-6-[2-(3-pyridyl)ethenyl]1, 3, 5-triazine (3a), leukotriene C4 (LTC4) antagonist, was found to possess a protective effect of HCl·ethanol-induced gastric lesions. Analogues of 3a were synthesized and evaluated for the effect as well as antagonistic activity against LTC4-induced contraction. Seven compounds (3a-d, f-h) exhibited a potent protective effect on gastric lesions which was considered to be based on the antagonistic activity against LTC4. The structure-activity relationships of the derivatives (3a-k) are discussed.