Objectives : In the present study, the effect of Kuwonsimsin-hwan (KSS) was tested in methotrexate (MTX)-induced immunosuppressed SD rats. Methods : Methotrexate was fed to white rats once a day for 4 days. After the immune responses of the rats deteriorated, dried extracts of Kuwonsimsin-hwan mixed in water was fed to the rats once a day for 14 days. We then measured the number of lymphocytes in peripheral blood and the percentage of B-cells, T-cells, CD3+CD4+T-cells, CD3+CD8+ T-cells and IL-2 productivity sampled from spleen and peripheral region. Results : (1) The number of lymphocytes and the percentage of T-cells and CD3+CD4+ T-cellsin peripheral blood increased significantly in the KSS group as compared with the control group. (2) The percentage of B-cells, CD3+CD8+ T-cells, and CD4+/CD8+ T-cells in peripheral blood were not different statistically. (3) The percentage of T-cells in spleen and IL-2 productivity of spleen cells increased significantly in the KSS group as compared with the control group. (4) The percentage of CD3+CD4+ T-cells in spleen increased in KSS the group as compared with the control group but without statistical significance. (5) The percentage of B-cells, CD3+CD8+ T-cells, and CD4+/CD8+ T-cells in spleen were not different statistically. Conclusion : It is concluded that Kuwonsimsin-hwan has immunostimulating effect on MTX-induced immunosuppressed SD rats.