Objectives: Avian Influenza has captured the attention of the international community over the years, with outbreaks in poultry having serious consequences on both livelihoods and international trade in many countries. Decreased efficacy of production and increased mortality rate are observed in affected flocks. Serological assays are useful tools to evaluate immune status of birds. Hemagglutination inhibition (HI) test is a serologic test which is commonly used in diagnostic laboratories. Material and Methods: In order to determine AIV (H9N2 subtype) antibody titers in broiler flocks of Gilan province,1247 blood samples were collected from 88 broiler flocks of Gilan province from April 2016, through March 2017,and subjected to HI. The results were recorded and analyzed using version 16.0 of SPSS statistical software. Results: Mean antibody titer for AI was 2.7. Minimum antibody titer was 0 and maximum antibody titer was 9. Two hundred sixty nine samples (21%) had antibody titers of 6-9 which may be due to field challenge of AIV. There were some differences in antibody titers status of birds between different seasons of year. Conclusion: High HI antibodies of AIV in serum of birds highlights important role of this infection in respiratory complexes of broilers in this area. Recently, circulation of highly pathogenic avian influenza (H5N8) viruses has confirmed in poultry flocks of this region. Cocirculation of these subtypes, H9N2 and H5N8, of avian influenza virus will affect the epidemiological pattern of both subtypes. Therefore, continuous investigations of prevalent viruses should be considered.

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