The number, external morphology and distribution of antennal sensilla of a predatory beetle, Trogossita japonica Reitter, were determined using scanning electron microscopy. A sexual dimorphism in antennal structure and in types and number of sensilla, indicative of their differential functions in the sexes, was apparent. The club segments have dense receptor fields composed of several distinct sensilla, and the terminal segment consists of a variety of sensory structures at maximum density. There was also a great difference in the numbers of certain types of sensilla on male and female club segments. A major difference occurred in the number of sensilla basiconica type 1, which are ≈150 in number, present on male terminal segment and none on the female. Sensilla basiconica type 3 on the terminal segment of the females were seven times more prevalent than in males, indicating their role in host volatile identification. A unique kind of sensilla basiconica pegs, with a terminal nipple and with several of them arranged in clusters in deep pits, were observed on the surface of the club segments in both sexes.