Drosophila albomicans is a species widely distributed but mainly in Southeast Asia. In its traditional distribution, there are substantial genetic differentiations among three geographic areas, Southeast Asian continent, Taiwan and Nansei islands. In the last decade, however, this species has invaded the Japanese mainland and is now spreading its distribution area to western Japan. In this study, variations of chromosomal arrangements, allozymes and sex ratio in F₂ hybrids with D. nasuta were examined to identify the origins of the newly colonizing population. The results strongly suggest that the origins of Japanese mainland population can be found in Taiwan.