Codonopsis lanceolatae has been used as one of the traditional remedies as well as food source. However, few studies on their immunomodulating effects have been reported. We previously reported that ex vivo supplementation of Codonopsis lanceolatae water extracts enhanced splenocyte proliferation compared to the control group. In order to elucidate its ex vivo effect, six to seven week old balb/c mice were fed ad libitum on a chow diet and water extracts of Codonopsis lanceolatae were orally administrated every other day for four weeks at two different concentrations (50 and 500 mg/kg B.W). After preparing the single cell suspension, the proliferation of splenocytes was determined by MTT (3- [4,5-dimethylthiazol-2-y] -2,5-diphenyl terazolium bromide) assay. The production of cytokine (IL-1${eta}$, IL-6, TNF-${alpha}$), secreted by macrophages stimulated with LPS or not, was detected by ELISA assay using a cytokine kit. After 48 hrs of incubation with the mitogen (ConA or LPS) stimulation, the mice splenocyte proliferation in experimental group was statistically increased at two different concentrations than that in control group. The cytokines production was more significantly enhanced at the lower supplementation (500 mg/kg B.W.) group rather than higher concentration (500 mg/kg B.W.) compared to the control group. The results of this study may suggest that the supplementation of water extract of plant mixture could regulate the immune function by increasing the splenocyte proliferation and enhance the immune function through regulating cytokine production capacity by activated macrophages in mice.