Effect of the butanol fraction of Astragali Radix (BFAR) on the humoral immune response were investigated in ICR mice. Mice were divided into 4 groups and BFAR at doses of 5,25 and 125 mg/kg were administered orally to mice daily for 3 weeks, and the normal animals were given vehicle. The results of this study are summarized as follows; the relative weight of spleen was markedly increased by BFAR treatment, compared with that in normal mice. However, the body weight gain and the relative weight of liver were not affected. Splenic plaque forming cells and hemagglutination titers to sheep red blood cells, and the secondary IgG antibody response to bovine serum albumin were also dose-dependently enhanced by BFAR treatment. In these mice, BFAR did not increase serum alanine aminotransferase total protein, sect albumin and albumin/globulin ratio when compared with those in normal mice. Thus, these findings indicate that BFAR significantly enhances humoral immune response to antigen in concentrations that do not affected liver function.