The accidentally introduced leaf beetle Ophraella communa LeSage has become widely dispersed over regions with different climates in East Asia, following its host plant—the alien invasive ragweed Ambrosia artemisiifolia. During this range expansion, some of its life history traits have changed in response to environmental conditions in newly-colonized habitats. In this study we examined genetic variation in mtCOI gene among nine geographical populations of O. communa in East Asia, including one from Japan, one from Korea and seven from China. Our analysis identified two distinct clades (C1 and C2) among these populations, C2 including only the Fujian population from China and C1 including the other populations; haplotype sequence divergence was as large as ≥ 3% between the two clades yet negligible within each of them. Our results suggest that the Fujian population of O. communa is distinctly diverged at mtCOI genetic level from the other populations.