Background : The β3-adrenergic receptor (β3-AR) and uncoupling protein 1 (UCP-1), expressed mainly in brown adipose tissue, are involved in the regulation of thermogenesis and lipolysis. Recent studies have shown that polymorphisms of the 3-AR (Trp64Arg) and UCP-1 (-3826, A to G) genes are associated with low basal metabolic rate (BMR) and obesity. Methods : We investigated the effects of the β3- AR and UCP-1 gene polymorphisms on body fat and energy metabolism in 65 normal Korean men aged from 21 to 36 years. The Trp64Arg mutation of the β3-AR gene and A to G polymorphism (-3826) of UCP-1 gene were detected by polymerase chain reaction (PCR)-restriction fragment length polymor- phism (RFLP) method. Results : In normal Koreans, Arg64 allele frequency of the β3-AR was 0.15 and the allele frequency of the A to G substitution of the UCP-1 gene was 0.48. No significant difference was found in BMR, body fat and abdominal fat amount in relation to β3-AR or UCP-1 genotypes. However, when the polymorphisms of the two genes were combined, the subjects with the polymorphisms of both UCP-1 and g-AR genes were found to have higher body mass index, higher total fat and abdominal fat amount, lower BMR, and lower fat oxidation rate when compared with the subjects without these polymorphisms. Conclusion : These results suggest that the polymorphisms of either β3-AR or UCP-1 gene alone did not significantly affect BMR, fat oxidation and body fat amounts, but both UCP-1 and β3-AR genes polymorphisms have synergistic effects on decreased basal metabolic rate, fat oxidation rate, and increased body fat in normal Korean adults.