We investigated energy metabolism enhancement by pepper by examining suppression of body fat accumulation in mice due to piperine (PIP) and black pepper (BP) intake. To induce adiposity, mice were fed a high-fat, high-sucrose (HFS) diet as a control diet for 4 weeks. Visceral fat weights decreased significantly in the mice fed diets of 0.03% and of 0.05% PIP. Body weight in the 0.05% PIP group also decreased significantly. In the mice fed a diet of 1.0% BP, body weight and visceral fat weights decreased significantly. For all parameters tested, the 1.0% BP group tended to show values slightly lower than those of the 0.03% PIP group. Expression of thermogenic protein uncoupling protein 1 tended to increase in the mice on the 1.0% BP diet. These results indicate that BP suppresses the effect of body fat accumulation mainly through the action of PIP.