Objectives : This study was designed to test the effect of a warm environment and Bujaijung-tang on immune and lipid metabolism in rats. Methods : The extract from Bujaijung-tang was made by the pharmacy department of Kyung-Hee oriental medical hospital. The animals were divided into four groups, by room or warm environment and Bujaijung-tang administration. Each group had 8 Sprague-Dawley Rats. We measured body temperature twice a week, body weight three times a week. After 3 weeks of experiment, serum lipid level, WBC, differential count, lymphocyte proliferation and immune cytokine concentration were measured. Results : 1. warm environment induced weight loss in rats. 2. warm environment induced a decrease of total cholesterol and low-density lipoprotein (LDL) cholesterol gain. 3. warm environment and Bujaijung-tang induced an increase of tumor necrosis factor (TNF)-${alpha}$ concentration. Conclusions : The warm environment had a hyperlipidemia modulating effect. The warm environment and Bujaijung-tang had an immune modulating effect.