The purpose of this research was to investigate the effect of Eunkyo-San(EKS) on the immune system. Administration of EKS(500 mg/kg) enhanced viability of splenocytes and thymocytes in BALB/c mice, and also EKS increased of splenic B, T lymphocytes and thymic T lymphocytes, significantly increased CD4 positive TH cells. EKS markedly enhanced the production of -interferon in mice serum. EKS accelerated the production of nitric oxide in peritoneal macrophages. These results suggest that EKS have an immune-enhancing activity.