Aralia cordata is known in traditional Korean medicine as a remedy for arthritis. As a part of our program to screen medicinal plants for potential anti-inflammatory compounds, oleanoic acid 28-O-β-Dglycopyranosyl ester (OA) was isolated from the roots of Aralia cordata. So, the immune modulation molecular mechanism of OA isolated from A. cordata was studied. One of the possible mechanisms for its protective activities is by down regulation of the inflammatory responses. Therefore, cells from the human mast cell line (HMC-1) were used to investigate this effect. OA significantly inhibits the way in which phorbol 12-myristate 13-acetate (PMA) plus A23187 induces the production of inflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-8 and intracellular Ca 2+ levels. In activated HMC-1 cells, phosphorylation of extra-signal response kinase (ERK) 1/2, degradation of IκB, and activation of NF-κB decreased after treatment with OA. OA suppressed the expression of TNF-α, IL-6 and IL-8 through a decrease in the intracellular levels of Ca2+ and ERK 1/2, as well as activation of NF-κB. These results indicated that OA exerted a regulatory effect on inflammatory reactions mediated by mast cells.