The MeOH extract of Asarum sagittarioides (Aristolochiaceae) showed antihistaminic activity. N-Isobutyl-3, 4-methylenedioxybenzamide (1) was isolated as the active principle, and this compound was proved to be an antiallergic substance by pharmacological studies. Furthermore, in order to investigate the structure-activity relationships, some analogues of 1 were synthesized, and compounds 4 and 5 were found to show more potent activity than 1.