Abstract: Partial sequences of the D-loop and the complete sequences of cytochrome b gene (1140 bp) of the slow lorises (genus Nycticebus) were undertaken to investigate evolutionary relationships among species of Nycticebus.Sequence analysis results consistently provide new taxonomy evidence at the DNA level for supporting Ratajszczak and Groves viewpoint that N.intermedus is merely the adult of N.pygmaeus (Ratajszczak,1998;Groves,1971).Phylogenetic analysis was performed by means of the combined data and these two separate sequences data,respectively,by using various methods,supporting the same topology,in which genus Nycticebus was formed of two clusters.The first cluster was composed of N.pygmaeus，and the second cluster of N.coucang.It also could provide a new molecular genetic evidence to support the view that the genus comprises two species:N.coucang and N.pygmaeus.