An anti-obesity effect was observed for cholest-4-en-3-one (cholestenone) which is an intestinal catabolite of cholesterol. Body weight gain and body fat accumulation of CDF 1 mice were inhibited by 0.5% dietary exposure to this chemical. Dose response for the effect of cholestenone was found to increase as the dose rose from 0.1 to 0.3% and 0.500. No obvious anomaly due to consumption of cholestenone was detected by necropsy and clinical observation. The mechanism of this effect of cholestenone is not known at present, but it was not due to anorexia.