The purpose of this research was to investigate effects of Samultang water extract (SMT) on cytokine production from immune cells during the late stage of pregnancy in BALB/c mice. SMT(500 mg/kg) was administered p.o. once a day for 7 days, and then thymocytes and peritoneal macrophages were separated. At the late stage of pregnant mice, the proliferation of thymocytes and the production of ${gamma}-interferon$ in thymocytes were decreased as compared with normal group, but the production of interleukin-2 and interleukin-4 was increased. The production of tumor necrosis $factor-{alpha}$, nitric oxide and phagocytic activity in peritoneal macrophage was increased as compared with normal group. At the late stage of pregnant mice administered with SMT, the production of interleukin-2 in thymocytes was decreased as compared with a pregnant group, but the proliferation of thymocytes, the production of ${gamma}-interferon$ and interleukin-4 was increased. The production of tumor necrosis $factor-{alpha}$ and nitric oxide in peritoneal macrophages were decreased as compared with a pregnant group, but phagocytic activity were increased. These results suggest that SMT has the regulative action on immune function of thymocytes and peritoneal macrophages at the late stage of pregnant mice.