Abstract: In order to provide evidence for taxonomy, evolutionary biology, biogeography and phylogenetics of the genusDugesia, the chromosomes and karyotypes of the freshwater planarians, Dugesia sp., collected from Shuhe town inLijiang City, Longwangtang pond in Baoshan City, and Xiaozhaongdian town in Xianggelila City, Yunnan Province,were studied. The adult planarians, 15—20 mm in length and 1.5—2.0 mm in width, were used. After starving for aweek, each planarian was transversally cut into five pieces, the planarian pieces were cultured in distilled water for threeor four days to regenerate. For the karyological analysis, the metaphase chromosomes were prepared from regeneratingblastemas by an air-drying method. Chromosome numbers of over 100 well-spreaded cells were counted and the chromosomeswere photographed using Leica DMLB light microscope. The karyotype parameters of five well-spreadedmetaphase plates from five individuals were measured. Relative length (r.l.) was calculated as chromosome length ×100/total length of haploid genome. Centromeric index (c.i.) was calculated as length of the short arm×100/ total length ofthe chromosome. Arm ratio (a.r.) was calculated as length of the long arm/that of the short arm. Mean values and standarddeviations (S.D.) were calculated from five metaphase plates obtained from a minimum of five fissiparous specimensfrom each experimental population. The karyotype were arranged firstly according to the gradually decreasinglengths of chromosomes and then the centromeric indices. The chromosomes were classified based on the criteria proposedby Levan, et al (1964). The results showed that planarians collected from Shuhe town had a diploid chromosomenumber of 16 with a karyotype formula of 2n=2x=16=16m. Planarians collected from Longwangtang pond had both thetriploid 24 (2n=3x=24=24m) and partial diploid 16 (2n=2x=16=16m), i.e, which were mixoploids. It was noteworthythat the planarians collected from Xiaozhaongdian town had a triploid aneuploid chromosome number of 26 with akaryotype formula of 2n=3x+2=24+2=21m+3st+2m, but a few were 25 (2n=3x+1=24+1=21m+3st+1m) or 24(2n=3x=24=21m+3st). The karyological results of the planarians collected from Xiaozhaongdian town were obviouslydifferent from those of Dugesia japonica and other species in Dugesia, The main factor that affected the karyologicalresults might be the change of environment (altitude, water temperature, atmospheric pressure and UV radiation). Perhapsit was the change of chromosomes and karyotypes that led to speciation and the evolution of species. Based on theresults of karyotype analysis of freshwater planarians, Dugesia sp., from the three places, classification of freshwaterplanarians and chromosome aneuploidy had been discussed in this paper. In order to obtain more precise karyologicaldata of Dugesia planarian, other sensitive techniques such as chromosome banding, fluorescent staining or in situ hybridizationshould be useful to get more evidence for taxonomy, genetics, evolutionary biology, biogeography and phylogeneticsof Dugesia.