BACKGROUND: Infection by infectious bursal disease virus (IBDV) in turkeys may  lead to immunosuppression effects and therefore turkeys could not resist against pathogenic or less pathogenic agents. OBJECTIVE: The aim of present study was to examine the effects of IBDV on response of turkey’s poults to avian influenza virus (AIV).METHODS: A total of 100 day-old poults were divided randomly into 4 equal groups. Groups 1 and 2 were infected with 104CID50 of IBDV by oral route at 1 day of age; groups 1 and 3 were infected with 106 EID50 of AIV (H9N2) by the oculo-nasal route at day 30. Poults of  group 4 were kept  as uninfected control group. All groups were vaccinated with Newcastle disease virus (NDV) vaccine. Blood  samples  via wing web were collected at days 0, 30, 37, 44, 51  and 58 and anti- NDV and anti-AIV serum titers were measured by HI test. At days 33 and 41 three poults of each group were euthanized and their splenic lymphocytes proliferation repose to phytohaemagglutinin was assessed. RESULTS: Influenza clinical signs were prolonged and more intensive in group 1 than group 3. The mean HI titers to NDV were significantly lower in group 1 than group 3, in all sampling times, but anti-AIV titers were significantly lower in group 1 compared to group 3  from days 14 AIV (H9N2) post infection. The lymphocyte proliferation assay with PHA did not show any differences between groups 1 and 3. CONCLUSIONS: IBDV suppresses immune response in turkey and causes prolonged and more intensive clinical signs after challenge with AIV.