Antifungal activity of tryptamine was tested using a causal agent, Corynespora cassiicola, of Corynespora leaf spot of cucumber. Tryptamine inhibited spore germination of C. cassiicola at dosage of over１２５０μg/mL. When cucumber plants（Cucumis sativus L. cv. Hokushin）at the２?leaf stage were inoculated with C. cassiicola in the presence of tryptamine（２５００μg/mL）, Corynespora leaf spot formation was significantly inhibited. Phytotoxicity was not observed even by tryptamine treatment at２５００μg/mL. Furthermore, tryptamine inhibited Corynespora leaf spot lesion formation in other cucumber cultivars. These results suggest that use of exogenous or endogenous tryptamine in cucumber contributes to protection of many diseases of cucumber.