This experiment was conducted to study serotype identification of the endemic strain of avian infectious bronchitis virus, Jin13, isolated recently from the infected chicken flocks in the suburbs of Zhengzhou city. Trachea organ cultures (TOC)neutralization,hemagglutination inhibition (HI), cross-ELISA based on the monoclonal antibody, sequencing, and immunization test were adopted in this study. Jin13 strain could react to the sera against M41 virus but not to the standard positive serum against NDV, EDS-76V, H9 AIV and IBDV in TOC and HI test, and sequence analysis confirmed that Jin13 strain virus is avian infectious bronchitis virus. Jin13 strain showed significant cross-reaction to the Massachusetts serotype M41 strain and H52 strain (0.25≤R≤0.8), but not to the nephropathogenic strain Y (R≤0.25) in TOC and cross-HI test. The results of cross-ELISA based on the monoclonal antibody indicated Jin13 strain had a significant response to J1 monoclonal antibody to M41 virus strain (≥640~1280) but not to the C2 monoclonal antibody to Y virus strain (≤40). These results further confirmed that Jin13 and respiratory-type M41 strain, H52 strain are the same serotype IBV. Compared with the M41 strain, S1 amino acid sequence of Jin13 strain had emergence of mutations in the sites 126, 386, 390, and 461. Moreover, a new restriction site, AIu I, occurred in the 1 166 site of the Jin13 strain S1 gene. These results suggested that Jin13 strain is a mutant strain of M41 IBV. Immunization test confirmed that immunogenicity of Jin13 was superior to that of M41 and H52 strain. Jin13 strain is an endemic strain of IBV with good immunogenicity.