The aim of this study was to investigate whether acteoside isolated from Clerodendron trichotomum Thunberg may act as a selective inhibitor of phospholipase $A_2$ in RBL-2H3 cells. Acteoside dose-dependently inhibited 0.5 ${mu}M$ melittin-induced release of [$^3H$]arachidonic acid, which was due to the inhibition of cytosolic $Ca^{2+}$-dependent phospholipase $A_2$ ($cPLA_2$) rather than secretory $PLA_2$ ($sPLA_2$). In Dixon plots, the apparent $K_i$ value of acteoside on $cPLA_2$ was 5.9 ${mu}M$ and the inhibitory pattern appeared to be a competitive inhibitor. The above data, suggests that acteoside acts as a competitive inhibitor of $cPLA_2$> in RBL-2H3 cells.