The karyotypes of the Drosophila robusta species-group, especially its species-subgroup okadai, were studied by using brain cell-Giemsa staining method. Drosophila gani possessed a diploid number of 12 chromosomes, comprising 4 pairs of metacentric and 2 pairs of acrocentric chromosomes, and both D. okadai and D. neokadai did 2n=12, with 3 pairs of metacentrics, 2 pairs of acrocentrics and 1 pair of microchromosomes. The okadai subgroup characteristically retained a middle-sized acrocentric × chromosome, which implies that this subgroup may occupy an ancestral position for the robusta group.