Abstract: Twenty-six samples of Rattus norvegicus from 8 localities in China were used for the investigation of the genetic polymorphism by means of mitochondrial DNA (mtDNA) RFLP analysis.The mtDNA of each sample was digested with 12 restriction endonucleases,ApaⅠ,AvaⅠ,Bam HⅠ,BclⅠ,BglⅠ,ClaⅠ,Eco RⅠ,Eco RⅤ,Hin dⅢ,PvuⅡ,ScaⅠ and XbaⅠ.The fragment patterns were examined by agarose gel electrophoresis or by Southern hybridization with DIG-labeled mtDNA probe.Twenty restriction morphs have been recognized,which can be grouped into 11 haplotypes.Extensive mtDNA polymorphism was found between individual animals,within and among populations of Chinese R.norvegicus.Almost each of populations had distinct mtDNA haplotype,some with more than one type.The divergence for the 11 detected haplotypes ranged from 0.2% to 1.4%,comparable to that previously reported for the rats from the United States,Japanese and the laboratory type.The findings are helpful for understanding the dispersion and evolution of this animal.