Several nutrition and food ingredients are supposed to have beneficial effects, but precise cell biological mechanism has not been elucidated. Among food ingredients, polyphenols such as soy bean isoflavon genistein and wine resveratrol have been reported to have effects on lipid metabolism and cardiovacular diseases (1). In order to elucidate the effect of genistein on obesity, we cultured adipocyte and observed of genisten to lipid accumulation in cells. Triglyceride accumulation was suppressed by genistein when it was added at the time of differentiation but not when added after differentiation. Genistein is considered to suppress lipid accumulation by suppressing the differtiation of adipocytes.