Abstract: Misgurnus anguillicaudatus and Paramisgurnus dabryanus are two common species of mud loaches in Hubei Province.A comparative study of the karyotypes in these two species was carried out with particular considerations on their taxonomy and evolution.The Chromosome preparations for this study were made with short-period PHA-cultured kidney cells in vitro by the air-drying method and Giemsa staining.Misgurnus anguillicaudatas has a diploid chromosome number of 100 with a fundamental arm number (NF) amounting to 128.Ilts karyotype comprises 8 pairs of metacentrics,6 pairs of submetacentrics and 36 pairs of telocentrics.Paramisgurnus dabryanus has 2n=48 with NF=64,which consists of 6 pairs of metacentrics,2 pairs of submetacentrics and 16 pairs of telocentrics.But cells containing 2n of 49 with NF of 65 were also found in some individuals collected from sha shi market.No sex chromosome was fourd in these two species.Basing upon the above mentioned results of karyotype analysis,one may well consider Misgurnus anguillicaudatus as a tetraploid fish which has been formed through a spontaneous polyploidization of chromosome complements from 2n(=50) to 4n(=100).Thus,the 2n of the primitive species should be 50.In fact,the 2n of the Japanese mud loach Misgurnus anguillicaudatas was reported to be 50,which has not been found in China.Regarding the karyotypical differences between Paramisgurnus dabryanus 2n=48(49) and the supposedly primitive species (2n=50),it might be due to some structural rearrangements such as Robertsonian translocations among chromosomes of the primitive form,which had occurred in the course of karyotypical evolution,resulted in the reduction in chromosome number.A smallest supernumerary chromosome found in Paramisgurnus dabryanus is probably a chromosome.Further studies,however,are needed to substantiate all these propositions.