Abstract: In order to determine the pathogenic agent of the chicken farm and to grasp the molecular characteristics and pathogenicity of the pathogen,infectious bronchitis virus-suspected clinical samples were detected in this experiment by RT-PCR,virus isolation,S1 gene sequence analysis,EID₅₀ determination,Newcastle disease virus interference test,and pathogenicity test. The results showed that the clinical samples were initially positive for IBV nucleic acid by RT-PCR. The isolated strains could cause the regular death of 10-day-old SPF chicken embryos,and the characteristic lesions of chicken embryos such as dysplasia,curling up and becoming smaller. The nucleotide sequence of S1 gene of isolated virus strain had more than 93.6% homology with that of S1 gene of QX type IBV strain in GenBank. In the genetic evolution relationship,the isolated strain was in the same branch as QX IBV strains which were prevalent in recent years,but in different branches with H120,M41,491 vaccine strains. The EID₅₀ of the isolated strain to SPF chicken embryos was 1×10^-5.68/0.1 mL,which could interfere with the hemagglutination titer of Newcastle disease virus. The isolated strain had a mortality rate of 70% for SPF chickens,and could cause typical symptoms of SPF chickens such as dyspnea,trachea hemorrhage,kidney enlargement and bleeding,and obvious spotted kidney. The results suggested that an epidemic strain of QX genotype IBV was successfully isolated from clinical samples.