isoimperatorin (4-[(3-Methyl-2-butenyl)oxy]-7H-furo[3,2-g][1]benzopyran-7-one) is a medicinal herbal product that is isolated from the dried roots of Angelicae dahuricae. Isoimperatorin inhibits the cyclooxygenase-2 (COX-2) and COX-1-dependent phases of prostaglandin $D_2;(PGD_2)$ generation in bone marrow-derived mast cells (BMMC) in a concentration-dependent manner, with $IC_{50}$ values of 10.7 ${mu}M$ and 24 ${mu}M$, respectively. However, this compound was not able to inhibit COX-1 and 2 protein expression in BMMC that were treated with concentrations of up to 50 ${mu}M$, which indicates that isoimperatorin directly inhibits COX-2 activity. Furthermore, this compound consistently inhibited the production of leukotriene $C_4;(LTC_4)$, as well as the degranulation reaction in BMMC, with an $IC_{50}$ value of 5.7 ${mu}M$ and 9 ${mu}M$, respectively, and these effects occurred in a dose dependent fashion. These results demonstrate that isoimperatorin has a dual cyclooxygenase-2 selective/5-lipoxygenase inhibitory activity, and therefore may provide the basis for novel anti-inflammatory drugs.