The water extract fraction of wasabi (Eutrema wasabi Maxim.) markedly suppressed the growth of MKN-28 human stomach cancer cells. When MKN-28 cells were cultured with more than 40 mul/ml of the water extract of wasabi, they were underwent morphological alteration with frequent cell death. The substances that suppressed the growth of MKN-28 cells were existed in the fraction consisting of components with molecular weights under 5000. The growth-inhibiting effect on MKN-28 cells was unaffected by treatment at 90-degrees-C for 10 min. Shinigrin and isothiocyanates which are main components of wasabi had no growth-inhibiting effect.