Objectives: Respiratory complexes are serious threats to poultry industry causing a heavy financialburden on the owners of the industry and governments. Avian influenza virus (AIV) and Newcastledisease virus (NDV) are the two most important respiratory agents in poultry production. Decreasedefficacy of production and increased mortality rate are observed in affected flocks. Serologicalassays are useful tools to evaluate immune status of birds. Hemagglutination inhibition (HI) test is aserologic test which is commonly used in diagnostic laboratories. Material and Methods: In order to determine NDV and AIV (H9N2 subtype) antibody titers inbroiler flocks of West Azarbayjan, blood samples were collected from 64 flocks of WestAzarbayjanavicultures and subjected to HI. The results were recorded and analyzed using version18 of SPSS statistical software. Results:Mean antibody titers for NDV was 9.4, at least of antibody titers was 7 and peak of antibody titers was 12,85% (425birds)had antibody titers range of 7-10 which may be due to previous vaccination and15%(75 birds)were in range of 11-12(possibility of field challenge).Mean antibodytiters for AI was 8.7,at leastantibody titers was 7 and peak of antibody titers was12 ,94%(470 birds)had antibody titers range of7-10which may be due to previous vaccination and 6%(30birds)were in range of 11-12 which possible showed field challenge.There were some differences in antibody titers status of birds between different season of year. Conclusion: High HI antibodies of AIV and NDV in serumof birds highlights important role ofthese infections in respiratory complexes of broilers in this area. Biosecurity measures, vaccinationand monitoring are effective tools to prevent introduction of such infections and decrease financiallosses due to these infections.

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