In a trapping study conducted in the experimental research forest of the Tohoku Research Center, Morioka, Honshu, Japan, we investigated the effect of heterospecific pheromone on pheromonal attraction of male Japanese gypsy moth, Lymantria disparjaponica (Motschulsky), and male pink gypsy moth, L. mathura Moore (Lepidoptera: Noctuidae: Lymantriinae). Traps baited with synthetic pheromone of L. d. japonica ((7R,8S)-cis-7,8-epoxy-2-methyloctadecane = (+)-disparlure (100 µg)) or L. mathura ((9R,10S,3Z,6Z)-cis-9,10-epoxynonadecadiene = (+)-mathuralure (20 µg) and (9S,10R,3Z,6Z)-cis-9,10-epoxynonadecadiene = (−)-mathuralure (80 µg)) attracted male L. d. japonica or L. mathura, respectively. Traps baited with synthetic pheromone of both species captured significantly fewer male L. mathura than traps baited solely with synthetic L. mathura pheromone. Numbers of male L. d. japonica captured in traps baited with (+)-disparlure were unaffected by the addition of L. mathura pheromone. (+)-Disparlure is a behavioral antagonist to pheromonal attraction of male L. mathura, whereas male L. d. japonica are indifferent to the presence of synthetic L. mathura pheromone.