Abstract: Levels of serum IgG of both normal mice and mice immunized with sheep red cell (SRBC) were markedly lowered after administration of Artemether, 100～200 mg/kg/d orally for 4～7 days. Mice infected with Plasmodium berghei did not show such immunopharmacological effects. The weight of spleen of normal and SRBC treated mice were significantly increased when treated with Artemether at doses of 100 up to 200 mg/kg/d given for 4～7 days. On the contrary, the spleen weight were significantly lower in the treated Plasmodium berghei infected mice than the untreated infected gruop which had markedly enlarged spleen. In comparison with the antimalarial drug Chloroquine given at the dose of 200 mg/kg/d for 4～7 days, it was found that the level of serum IgG and spleen weight were within normal range in Chloroquine treated mice in both the SRBC immunized and norrnal mice. However, in the infected mice, Chloroquine was effective in suppressing Plasmodium parasite in blood and preventing increase in spleen weight without altering the serum IgG level. It is concluded that Artemether possesses humoral immuno-suppressive effects in addition to antimalarial activity.