BACKGROUND: The age-related loss in muscular function is typically accelerated after menopause. Resistance training (RT) has been shown to increase muscle mass and strength in postmenopausal women. Branched-chain amino acid (BCAA) supplementation acutely increases myofibrillar protein synthesis (MPS) and decreases muscle soreness following RT. However, the combined effects of BCAA supplementation and RT on muscle mass, strength, and regulatory factors on postmenopausal cohorts are currently unknown. The purpose of this study was to explore the combined effects of BCAA supplementation and RT on muscle mass, strength, and regulatory factors in postmenopausal women. METHODS: Thirty postmenopausal women were randomly assigned to one of three conditions: RT and placebo (PLA; n = 10), RT and BCAA (BCAA; 9 g/day; n = 10), or control (CON; n = 10). Muscle mass, strength, and serum concentrations of muscle regulatory factors (myostatin, follistatin, and insulin-like growth factor-1 [IGF-1]) were assessed before and following 8 weeks of whole-body supervised RT (3×/week, 3-4 sets using 60-75% 1-repetition maximum [1-RM]). RESULTS: There were significant increases (P < 0.05) in muscle mass and strength in both the PLA and BCAA conditions. Additionally, myostatin significantly (P < 0.05) decreased, while IGF-1 (P < 0.05) increased following PLA and BCAA. However, follistatin significantly increased in the BCAA condition. There were no differences between RT conditions over time. Furthermore, there were no changes in any variable after CON. CONCLUSIONS: Short-term (8 weeks) RT is an effective intervention for improving muscle mass, strength, and muscle regulatory factors in postmenopausal women. The addition of BCAA supplementation to RT failed to augment these physiological changes.