RESUMO
Cystic echinococcosis is one of the most widespread and severe zoonotic helminthic diseases .To understand the phylogeny and genetic polymorphism Echinococcus granulosus (E .granulosus) prevailed in south region of Qinghai Prov-ince ,partial fragment of cytochrome oxidase Ⅰ (COX Ⅰ ) gene sequences were used to infer the phylogenetic relationship of 59 collected samples of E .granulosus in Qinghai Province .Total 72 sequences (13 sequences from GenBank) were aligned using CLUSTAL X ,and then ,Bayesian analyses were performed in Mrbayes-3 .1 .2 .The results revealed that Echinococcus spp .isolates did not form a monophyletic group .The most samples clustered with E . granulosus strain (G1) (AB297617) , but showed high genetic polymorphism .Another three samples clustered with E .multilocularis (AB018440) ,while they showed complex phylogenetic relationships among them ,further indicating that Echinococcus spp .isolates from Qinghai Prov-ince may has a more complex evolutionary history than expected .