In this study, thirty-one broiler chicken flocks were monitored for determining the most prevalent subtype of Avian Influenza Virus (AIV) circulating in the field. It was found that, the monitored broiler flocks suffered from clinical manifestation suspected to be infected with highly pathogenic Avian Influenza Virus (HPAIV). Three hundred and ten tracheal swabs
were collected from moribund and freshly dead birds for isolation and detection of AIV using Specific Pathogen Free Embryonated Chicken Eggs (SPF-ECEs) and through RRT-PCR. Twenty-seven out of thirty-one samples (27/31) gave haemagglutination activity after isolation in SPF-ECEs. By using Real time Reverse Transcriptase Polymerase Chain Reaction
(RRT-PCR), Ten out of thirty-one samples (10/31) were found to be positive for HPAIV (H5) and there was no detectable AIV (H7). Mixed infection of more than one virus was common in the monitored farms where, (AIV H5 and Newcastle disease virus (NDV)) were found to be positive in 3/31, (AIV H9 and NDV) were positive in 11/31, (AIV H5, H9 and NDV) were
found in 7/31. While the mono infection was rare where 3/31 were positive for AIV (H9) only, 3/31 were positive for NDV only and 4/31 were found to be negative for the previously tested viruses. From the afforded mention results, it could be concluded that subtype H9 of AIV was the most prevalent AIV subtype in Egypt.