To clarify the presence of a pheromone in Brontispa longissima (Coleoptera: Chrysomelidae), we observed its mating behavior and conducted a series of bioassays. When male and female B. longissima came in contact, the male was observed to hold and mount the female, extend its penis toward her abdominal tip, and copulate. The male was observed to hold the female only after he had touched her with his antennae and/or forelegs. Males showed similar mating attempts toward females killed by freezing. On the other hand, no males showed mating attempts toward females washed with hexane, but they did toward females washed with hexane and re-treated with hexane extract of the female body or female elytra. Furthermore, males showed similar mating attempts toward a glass dummy treated with a solvent extract of female elytra. These results indicate the presence of a female sex pheromone that is perceptible by direct contact and plays an important role in mating in B. longissima. When the crude extract of female elytra was subjected to silica gel chromatography, only the fraction eluted with hexane elicited mating behavior in males. Furthermore, when the active fraction was chromatographed on AgNO₃-impregnated silica gel, only the fraction eluted with hexane elicited mating behavior in males. The contact sex pheromone of B. longissima is therefore believed to consist of one or more less-polar compounds, probably saturated hydrocarbons.