Abstract: Chromosome numbers and karyotypes of seventeen populations of Allium wallichii(Alliaceae) from the Yunnan-Guizhou Plateau were examined.The polyploidy distribution pattern of this species was analyzed based on 412 newly studied plants from seventeen populations and published data.Nine diploid populations and six diploid-tetraploid mixed populations occur in central to northwest Yunnan,while twelve tetraploid populations occur in the Yunnan-Guizhou Plateau.Diploids are 2A type except ’Shangri-La d’and Baoshan populations which are 3A type,tetraploids are 2A type except Huize and Hezhang populations which are 2B type.The asymmetry index(AI) comparison indicates that the tetraploids in northwestern Yunnan are likely to be more ancient than those in other areas.The karyotype similarity of diploids and tetraploids indicates a possible autopolyploid origin of tetraploids in this species.