This research was performed in order to investigate the anti-inflammatory effects of Bupleuri Radix(BR) on the Immune response in vitro. Cellular proliferation and cytokine production were measured in mast cells or mouse B cells or CD4 Th cells. BR water extract inhibited the secretions of TNF-$alpha$ and IL-6 in PMA/A23187 stimulated HMC-1 cells. It increased proliferation but did not affect the expressions of CD69 or CD23 in rIL-4/anti-CD40 activated S cells. BR reduced surface IgE expression and secreted IgE but increased the production of IL-4, IFN-$gamma$ and IgG1 in the same cells. BR caused an increase in proliferation in anti-CD3/anti-CD28 stimulated CD4 Th cells but it did not affect the differentiation of Th1 or Th2 cells. However, IL-2 was increased in BR treated Th2 cells. Considering the above-mentioned results, BR can be applied to a broad range of anti-inflammatory reactions, but our data suggest that it will not be likely to exert any effects on type 1 allergic response.