Objectives This study is to investigate how dose Ikhwang-San can be effective on SD rats which deteriorated immunity caused by methotrexate. Methods The test sample were dosed once a day for 14 days by gastric gavage at the beginning of dosage 1000, 500 and 250㎎/㎏/10㎖ from 2 days after last MTX-dosing, and the changes of the body and spleen weight, total number of blood leukocytes, total number of lymphocytes, the percentage of B-cell, T-cell, CD3+CD4+ T-cell, CD3+CD8+ T-cell and CD4+/CD8+ T-cell ratios in the blood and spleen were observed. Results The changes of the body and spleen weight, the total number of blood leukocytes, the total number of lymphocyte in the blood and spleen were significantly increased in IHS Extracts groups comparing with the control group. The percentage of B-cell, T-cell, CD3+CD4+ T-cell in the blood and spleen were significantly increase in IHS groups and comparing with the control group. The ratio of CD4+/CD8+ T-cell in blood and spleen was significantly increased in IHS Extracts groups comparing with the control group. Conclusions According to those results, Ikhwang-San has good immunostimulating effect on SD rats which had deteriorated immunity caused by methotrexate.