Effects of capsaicin, a pungent principle of hot red pepper, were studied in the brown adipose tissue of rats fed a high-fat diet. Rats were divided into three groups : 1) nonpurified diet group (NP : n=12) , 2) high-fat diet group (HF : n=10) and 3) high-fat plus capsaicin diet group (HFC : n=10) . NP group was fed 15.4g diet/day. HF and HFC groups were fed 10.5g diet/day. Rats were fed each diet for 1O days. In body weight, NP group was heavier than HF and HFC groups. HF group was heavier than HFC group. In weight of the interscapular brown adipose tissue (IBAT) , HF group was heavier than NP and HFC groups ; HFC group was heavier than NP group. In the IBAT tissue weight/100g body weight, HF group was heavier than NP and HFC groups.But no difference was observed between HF and HFC groups. In both of the epididymal and the perirenal adipose tissue weights,HF group was heavier than NP and HFC groups. No difference was observed between NP and HFC groups. Serum glucose level of HF and HFC groups was lower than that of NP group. Serum free fatty acid level of HF and HFC groups was higher than that of NP group. In oxygen consumption ,HF group was lower than NP group and HFC group was lower than NP group when expressed per 100mg wet weight ;HFC group was higher than HF group when expressed per 100mg wet weight and per 10mg protein, respectively. Significant negative correlations were found between the IBAT oxygen consumption per 1Omg protein per hour and the epididymal or the perirenal adipose tissue weight. These results indicated that capsaicin lowers the epididymal and the perirenal adipose tissue weights and prevents decrease of the IBAT oxygen consumption as the result of high-fat diets effect.