This study examined sequence differences in mitochondrial cytochrome c oxidase subunit(cox1),large subunit ribosomal RNA (rrnL) and NADH dehydrogenase subunits 1 and 4 (nadl and nad4) between Chabertia ovina and C.erschowi from yaks in Qinghai and goats in Shaanxi provinces,China.A part of the cox 1 (pcox 1),rrnL (prrnL),nad1 and nad4 genes (pnad1 and pnad4) were amplified separately from individual nematodes by PCR and sequenced.The length of the sequences ofpcox1,prrnL,pnadl and pnad4 was 441 bp,450 bp,526 bp and 914 bp for C.ovina,and 441 bp,451 bp,?517 bp and 810 bp for C.erschowi,respectively.The intra:specific sequence variations within C.ovina were 0.2%:2.9% for pcox1,0:0.9% for prrnL,0.6%:2.3% for pnad1,and 0.4%:2.0% for pnad4,and were 0.5%: 1.6% for pcox1,0:1.1% for prrnL,0.2%: 1.7% for pnad1,and 0.4%: 1.1% for pnad4 within C.erschowi.Whereas,the inter:specific sequence differences between the two species were obviously higher,being 11.6%: 12.9% for pcox1,9.8%: 11.1% for prrnL,14.4%: 15.9% for pnadl,and 16.4%: 17.7% for pnad4.Phylogenetic analyses using Bayesian inference (BI),based on combined sequences of four genes,indicated that the C.ovina and C.erschowi represent distinct species.These results demonstrate that these mt gene sequences provide novel genetic markers for the identificaiton and differentiation C.ovina and C.Erschowi,and have implications for studying the population genetics and molecular epidemiology of Chabertia spp.