ABSTRACT
Karyotypes of nine species of Rattus from the mainland of South Vietnam and one from Thailand are presented. Members of the subgenus Rattus, including Rattus argentiventer, Rattus exiguus, Rattus exulans concolor, Rattus nitidus, Rattus norvegicus, Rattus rattus molliculus and Rattus sladeni, had diploid numbers of 42 and very similar karyotypes. Rattus surifer finis and Rattus moi, both in the subgenus Lenothrix, had identical diploid numbers, 52, but dissimilar karyotypes. The karyotype of Rattus sabanus revertens from South Vietnam was similar to that of Rattus sabanus reported from Malaysia.