Branched chain amino acids (BCAA) - leucine, isoleucine and valine are essential amino acids which are metabolized directly in muscles and offer energy fuel to performance of the work. There is lot of evidences supporting the positive effect of BCAA supplementation on muscle growth. The main importance is attached particularly to leucine. There was observed that leucine supplementation increased protein synthesis in skeletal muscles after resistance exercise in young people and in elderly people suffered by sarcopenia as well. There is not exactly clear, what is the reason for the positive effect of BCAA to increase protein synthesis in muscles. Besides the positive effect of BCAA on muscle growth, there was observed their positive effect against fatigue and on a production of endogenous glucose, which is necessary to maintain the glucose balance in body during adaptation to stress. The minimum and maximum dose of BCAA is not established, but the daily recommended amount of leucine : isoleucine : valine is in a ratio 40:20:20 mg.kg body weight -1. It is recommended to use the mixture of BCAA rather than leucine individual, because of depletion other BCAA in body. There was observed no toxicity of BCAA even at high doses. The present review describes the metabolism of action and effect of BCAA on protein synthesis and physiological functions in human.