A coumestan derivative, psoralidin (1) was found to be a cytotoxic principle of the seeds of Psoralea corylifolia L (Leguminosae) with the IC_{50}$ values of 0.3 and 0.4 ug/ml against the HT-29 (colon) and MCF-7 (breast) human cancer cell lines, respectively. A coumarin, angelicin (2) was also isolated as a marginally cytotoxic agent along with an inactive compound, psoralene (3) from the plant. The isolates 1-3 were not active against the A54l(lung) and HepG2 (liver hepatoma) cancer cell lines.