The genitalia of the Japanese species of Anthrax (5 species) and Brachyanax (1 species) are studied for the first time. The male genitalia of Anthrax are furnished with useful specific characters in many structures. One of them is a dorsal sclerite just before the gonostyli, and this sclerite varies markedly between species. Besides the spermatheca and genital furca, which are peculiar to each species, various segments of the female genitalia (e. g., tergum 8, sternum 8, etc.) vary considerably with species and it is taxonomically desirable to study them in every species of Anthrax.