To understand anti-allergic effect of Curcuma aromatica (family Zingerberaceae), which inhibited passive cutenous anaphylaxis (PCA) reaction in preliminary study, we isolated its main constituents, curcumin, demethoxycurcumin and bisdemethoxycurcumin, and investigated their inhibitory effects against PCA reaction and scratching behavior. These curcuminoids inhibited the PCA reaction induced by the IgE-antigen complex (IAC) and the scratching behavior induced by compound 48/80. These curcuminoids also inhibited degranulation, protein expression of TNF-$alpha$ and IL-4, and transcription factor NF-${kappa}B$ activation in IAC-induced RBL-2H3 cells. Of these curcuminoids, curcumin exhibited the most potent inhibition, followed by demethoxycurcumin and bisdemethoxycurcumin. These findings suggest that curcuminoids, particularly curcumin, can improve the symptoms of allergic diseases, such as anaphylaxis and itching.