Epimedii Herba is an important traditional herb medicine widely used as a tonic. However, the mechanism of action of this drug on the immune system is not well studied. This study was performed to elucidate the effects of the aqueous extract of Epimedii Herba on the production of antibodies in mice. Antibodies in serum were detected in male ICR mice treated with the aqueous extract of Eplmedii Herba (AEEH) at a dosage of 40, 120, and 360mg/kg orally for 2 weeks. Effects of oral administration of AEEH on antibody forming responses were measured by enzyme linked immunosorbent assay (ELISA) of immunoglobulin (Ig) levels in serum. The results were as follows; 1. Epimedii Herba slightly decreased body weight gain. 2. Epimedii Herba significantly increased the relative spleen weight. 3. Epimedii Herba significantly increased total serum IgG levels. 4. Epimedii Herba significantly enhanced total serum IgG1 levels. 5. Epimedii Herba significantly increased total serum IgG2a levels. 6. Epimedii Herba markedly increased total serum IgM levels. These findings demonstrate that Epimedii Herba significantly enhances the production of antibodies at therapeutic concentrations, and suggest that administration of Epimedii Herba may prevent the host from immunologic diseases.