BACKGROUND AND OBJECTIVES: Many patients develop a prolonged decrease of muscle strength after total hip arthroplasty (THA) despite their reconstructed hip joint. Physical exercise combined with branched-chain amino acid (BCAA) supplementation has been reported to improve muscle strength in elderly persons with sarcopenia. However, the effect of BCAA supplementation in patients after THA is unknown. This study examined the effects of BCAA supplementation combined with exercise therapy on the improvement of physical function in elderly patients after THA. METHODS AND STUDY DESIGN: The subjects were 31 elderly women who underwent THA. The participants were randomly assigned to two groups: BCAA (n=18) and control (n=13). The combined therapy was carried out for one month after THA. For the exercise intervention, a 3-set physical exercise program was conducted. For the nutritional intervention, the participants consumed 3.4 g of BCAA supplement or 1.2 g of starch immediately after the exercise intervention. RESULTS: BCAA supplementation combined with muscle strengthening exercises had a significant effect on knee extension strength of the contralateral side and on upper arm cross-sectional area. The improvement ratio of knee extension strength before and after intervention on the operated side was also significantly higher in the BCAA group. CONCLUSIONS: BCAA supplementation is effective for patients to improve the strength of some muscles when combined with physical exercises, but hip abductor muscle strength of the operated leg did not improve. A future study is needed to determine the efficacy of this combined therapy for hip abductor muscle strength.