Researchers are still discussing the classification of Nycticebus. We established a molecular phylogeny covering all recognized taxa in Nycticebus to provide information for further evaluation. We sequenced partial D-loop (ca. 390 bp) and cytochrome b genes (425 bp) from 22 specimens. We separated most of the major groups except for some mixing of Nycticebus. coucang coucang and N. bengalensis. Nycticebus pygmaeus diverged earlier from the ancestral stock than the other taxa. Nycticebus coucang menagensis was well discriminated from N. c. coucang. It may be possible to explain the mixing of Nycticebus coucang coucang and N. bengalensis by the hybridization between the 2 groups in the field. Although our data did not provide direct evidence for or against the new proposal that Nycticebus coucang javanicus be raised to the rank of a distinct species (N. javanicus), we have good evidence for regarding N. c. menagensis as a species.