In this study, the effect of 70% ethyl alcohol fraction of Cervus nippon(CN-E) on mouse T-lymphocyte was investigated in vivo. The administration of CN-E(100 mg/kg) enhanced the proliferation of thymocytes, the population of $CD4^+CD8^-$ single-positive cells and the production of $interferon-{gamma}$ in thymocytes and splenocytes. The administration of CN-E did not induce DNA fragmentation and reduce mitochondrial transmembrane potential in thymocytes. These results indicate that the CN-E contams a stimulative component on the proliferation of thymocytes, the population of $T_H$ cells and the production of $interferon-{gamma}$ in T-lymphocytes.