In the course of a searching natural antifungal compounds from plant seeds, we found that the methanol extract of Psoralea corylifolia seeds showed potent control efficacy against tomato late blight caused by Phytophthora infestans and wheat leaf rust Puccinia recondita. Under bioassay-guided purification, we isolated two furanocoumarins, psoralen and isopsoralen, with anti-oomycete activity against P. infestans. By 1- day protective application, both compounds strongly reduced the disease development of P. infestans on tomato seedlings, but hardly controlled development of leaf rust on wheat seedlings. This is the first report on the anti-oomycete activity of P. corylifolia as well as that of psoralen and isopsoralen.