Objectives : A traditional herbal prescription, Kyung-Ok-Ko (KOK), has long been used in oriental medicine as an invigorant for age-related diseases, such as amnesia and stroke. However, the beneficial value of KOK for immune responses is largely unknown. Based on the above mentioned effects of KOK, other previous reports, and its use in traditional medicine, we hypothesized that KOK displays beneficial effects against methotrexate (MTX)-induced immune suppression. Methods : We investigated the effects of KOK (0.6 g/kg/day, oral (p.o.)) on deteriorated immunity caused by MTX (2 mg/kg/day, p.o.) in an immune suppression mouse model. MTX was fed to mice once a day for 7 days. After the immune responses of the mice deteriorated by MTX treatment, KOK in water was fed to the mice once a day for 14 days. We then measured the expression levels of various cytokines, such as T helper cell (Th1, Th2) cytokines, and the number of immune cells, such as spleen T cells, B cells, and macrophages. Results : The data showed that MTX decreased Th1 profiles (interferon (IFN)-, interleukin (IL)-2, IL-12) and the number of immune cells, and increased Th2 profiles (IL-4, IL-5, IL-13), which were normalized significantly by post-administration of KOK. However, there was no significant difference in body-weight gain between MTX- and KOK-treated mice. Conclusion : These results indicate that KOK has immune-enhancing functions and reduces immunotoxicity of MTX, suggesting that supplementation with KOK will improve immune responses clinically and be useful for the prevention of immune-related diseases.