Objectives: The cortex and root of Acanthopanax sessiliflorus (AR), a herbal medicine, have been used for several diseases including cancer in Oriental countries. Recently, we reported that AR has an immune-potentiating action. Oga-Power(OP) was made using extract from AR. For these reasons, we hypothesized that OP can potentiate the immune system in terms of accelerating proliferation rates of immune cells such as thymocytes and splenocytes. Methods: In this experiment, proliferation rates of thymocytes and splenocytes were measured using modified 3-[4,5-dimethy -lthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT). No production levels in macrophages isolated from normal mice were measured using Griess method. Results: In our results, treatment with OP accelerated proliferation rates of splenocytes, but did not affect those of thymocytes in vitro. On the other hand, proliferation rates of thymocytes was elevated in vivo. In addition, level of NO production from macrophage separated from abdominal cavity of normal mice was elevated by treatment with OP. Conclusions: In conclusion, OP has immune-potentiating action, by acceleration of splenocyte proliferation and elevation of NO production level from macrophages.