Objective To study the effects of PEC, the oral liquid,which consists of Panax quinquefolium L, Epimedium brevicornum Maxim, Schisandra chinensis Bail and Cervus eplaphus L, on immune system in mice. Methods Lymphocyte proliferation assay and hemolysin concentration (HC 50 ) test were used,clearance rate of charcoal particles and DCH response induced by DNCB were determined. Results Application of 10-20 ml/kg of PEC promoted the lymphocyte proliferative activity, that of 2 5-10 ml/kg of PEC increased the production of serum specific antibody hemolysins, as well as it also enhanced clearance rate of charcoal particles, increased the phagocytic activity of the monocytes when it was given orally for 6-10 days. 2 5-10 ml/kg of PEC improved obviously the DCH response induced by DNCB in immune_suppression mice when it was given orally for 10 days. Conclusion PEC showed the strong immune_stimulating activities in mice.\;