Abstract: 【Objective】A nucleoprotein-based enzyme-linked immunosorbent assay for the detection of antibodies against infectious bronchitis virus.【Method】The purified recombinant IBV nucleoprotein was coated onto the Polystyrene plate and sealed up with confining liquid. Then the serum sample was added on it and incubated at 37℃ for 1 hour. When the plate was washed, the rabbit anti-chicken IgG labeled with HRP was put onto it for being incubated at 37℃ for 1 hour too. And then the substrate was added for coloring. OD value was assayed after the reaction being ended.【Results】The optimal concentration of coating antigen was 1.45μg/ml, and the optimal dilution of serum and rabbit anti-chicken IgG labeled with HRP were 1:40 and 1:1000 respectively. The detection-limit between negative and positive serum in OD450 value was 0.310, when the OD450 value was equal or over 0.314, it was positive, or else negative. NP-ELISA had no reaction to the positive serums of AIV H9、H5、H7、ND、IBD and EDS76 , which directed that the expressed NP protein was only reacted to the serum of IBV. 【Conclusion】The results above indicated the NP-ELISA afforded strong specificity, high sensitivity , excellent coincidence and could be used for antibody surveillance of IB in clinical practice.