Capsinoids are less pungent capsaicin analogues that increase whole body energy expenditure and hence reduce fat. Several studies have suggested that capsinoids activate brown adipose tissue (BAT), a major site of adaptive thermogenesis, but the actual contribution of BAT and uncoupling protein 1 (UCP1), a thermogenic protein expressed in BAT, to the fat-reducing effect of capsinoids has not yet been determined. Here, we investigated the effect of capsinoids on high-fat diet (HFD)-induced obesity using wild-type (WT) and UCP1-deficient (KO) mice. Capsinoids feeding potently suppressed HFD-induced increase in body weight, adiposity, and fatty liver development in WT mice. In contrast, such effects of capsinoids were completely abolished in UCP1-KO mice. Moreover, capsinoids significantly increased UCP1 protein expression in BAT without its apparent induction in white adipose tissue (WAT) in WT mice. These results indicate that capsinoids suppress diet-induced obesity of mice through the UCP1 function in BAT but not in WAT.