Branched-chain amino acid (BCAA) comprise of a group of essential amino acid that includes leucine, isoleucine and valine. As such, these amino acids are obtained exclusively from dietary sources and cannot be synthesized by the body. BCAA are commonly consumed as a supplement, but their impact on the immune system under basal and inflammatory conditions are ill-defined. To investigate the effects of BCAA on the immune system, we fed C57BL/6 mice a control AIN93G diet, or a diet containing 200% BCAA content relative to AIN93G. We performed comprehensive immunophenotyping of various organs including spleen, thymus, peripheral lymph nodes as well as intraperitoneal cavity. Our preliminary data shows that increased BCAA intake could alter CD4:CD8 ratio, as well altering regulatory subsets including Tregs and Bregs. BCAA intake had limited or no effect on proportion of innate immune subsets. Consumption of excess BCAA can alter the balance of key immune subsets under steady state conditions, which may have consequence under inflammatory conditions.