Methyl gallate (MG) is a medicinal herbal product that is isolated from Paeonia lactiflora that inhibits cyclooxygenase-2 (COX-2) dependent phases of prostaglandin $D_2;(PGD_2)$ generation in bone marrow-derived mast cells (BMMC) in a concentration-dependent manner with an $IC_{50}$ values of $17.0;{mu}M$. This compound also found inhibited the COX-2-dependent conversion of the exogenous arachidonic acid to $PGD_2$ in a dose-dependent manner with an $IC_{50}$ values of $190;{mu}M$, using a COX enzyme assay kit. However, at concentrations up to $80;{mu}M$, MG did not inhibit COX-2 protein expression in BMMC, indicating that MG inhibits COX-2 activity directly. Furthermore, MG consistently inhibited the production of leukotriene $C_4;(LTC_4)$ in a dose dependent manner, with an $IC_{50}$ value of $5.3;{mu}M$. These results demonstrate that MG has a dual cyclooxygenase-2/5-lipoxygenase inhibitory activity, which might provide the basis for novel anti-inflammatory drugs.