Abstract: Since 1998, H9N2 AI outbreaks have been one of the major problems in Iranian poultry industry. The association of high mortality and case report of H5N1 and H9N2 influenza virus in wild birds in recent years raised the specter of a possible new genetic modified AI virus. In this study, we do phylogenetic analysis on Full- length Nonstructural (NS) genes of seven H9N2 Isolates from Broilers in Iran, Tehran province during 1998-2007. Phylogenetic analysis clearly shows that Iranian H9N2 isolates gene pools, corresponding to just NS allele A. Comparison of nucleotide sequences of isolated viruses revealed a substantial number of silent mutations, which results in high degree of homology in amino acid sequences. In addition, the cluster of Iranian H9N2 isolates could be subdivided into two subgroups, which matched their times of isolation especially around 2006 time line. The high degree of similarity between the NS genes of the Iranian H9N2 isolates supports the hypothesis that these genes originated from a single predecessor. Present result provides useful molecular epidemiological data to understand the dynamics of H9N2 evolution during 9 years in Iran and support earlier phylogenetic observations.