Lambertianic acid is a bioactive diterpene found in the leaves of Thuja orientalis. Its effect on the bone marrow-derived mast cell (BMMC) mediated allergy and inflammation mechanism remains unknown. In this study, lambertianic acid was evaluated for its effect on the allergic mediators, including prostaglandin D(2) (PGD(2)), leukotriene C(4) (LTC(4)), β-hexosaminidase (β-Hex) and cyclooxygenase-2 (COX-2) protein, in phorbol 12-myristate 13-acetate (PMA) plus calcimycin-stimulated BMMCs. The results revealed that lambertianic acid inhibited the production of interleukin-6 (IL-6), PGD(2) and LTC(4), the expression of COX-2 and the degranulation of β-hexosaminidase in the PMA plus calcimycin-induced BMMCs. Taken together, these findings implied that lambertianic acid may possess the potential in the treatment of allergy.