Abstract: This paper presents comparative studies of the karyotypes of three species of Neoaplectana nematodes.The karyotypes of the gonadal cells and the ombryonic cells of N.glaseri(NC513,85011),N,carpocapsae (DD-136) and N.bibionis were studied.Slides were made by the squash techniquc with orcein staining.The results obtained from this study indicate that three species of ncmatodes show a 2N condition of nine chromosomes for the males,ten for the females,but they are different in karyotypes from one species to another.(The karyotype formulae):N.glaseri (NC513,85011)2n=4m+6t(♀)2n=4m+5t(♂);N.carpocapsae (DD-136)2n=8m+2t(♀)2n=7m+2t(♂);N.bibionis 2n=6m+4t(♀)2n=5m+4t(♂).In the last part of this paper,we compared and analyzed the karyotypes of three species and discussed the evolutionary relationship of their karyotypes.