Clonorchis sinensis infection is carcinogenic to human， which results in cholangiocarcinoma， confirmed by the World Health Organization. An investigation in 2005 indicated that the standardized C. sinensis infection rate was 0.58%， with 12 490 000 infected people estimated in the clonorchiasis endemic areas in China. In the world， 80% of C. sinensis infected people were distributed in China. Diagnostic Criteria for Clonorchiasis （WS309-2009） was compiled by the ex?Ministry of Health of the People’s Republic of China and it was issued and implemented in March 13， 2009. The Diagnostic Criteria for Clonorchiasis is composed of six chapters， including the Range of Application， Terms and Definitions， Diagnostic Basis， Diagnostic Principle， Diagnostic Standard， and Differential Diagnosis. Three informative appendices （etiology， epidemiology， clinical manifestation； enzyme?linked immunosorbent assay； differential diagnosis） and one normative appendix （laboratory examination） are appended. The Criteria provides the technical reference for diagnosis of clonorchiasis in medical institutions and disease control institutions. Combined with the current epidemic situation of clonorchiasis in China， this paper interprets the main contents of the Diagnostic Criteria for Clonorchiasis （WS309-2009）， so as to promote its learning and implementing.