Infectious coryza (IC), caused by Avibacterium paragallinarum, poses a significant economic threat to the global poultry industry. Although IC is present in Iran, there is limited molecular data characterizing the circulating strains, particularly regarding key hemagglutinin genes such as hagA. This study aimed to investigate the genetic diversity and phylogenetic relationships of Av. paragallinarum isolates recovered from commercial and backyard poultry in Iran by sequencing the hagA gene and comparing the findings with global strains. Twenty-three Av. paragallinarum isolates collected from Iranian poultry farms underwent PCR amplification and sequencing of the hagA gene. Nucleotide and deduced amino acid sequences were analyzed for homology, subjected to BLAST searches, and used for phylogenetic reconstruction. The isolates showed high sequence identity, ranging from 94.1-99.9% at the nucleotide level and 92.1-100% at the protein level. Phylogenetic analysis classified the isolates into five distinct clusters (Iran-1 to Iran-5). The largest cluster (Iran-1) showed a strong affiliation with strains from China and India, while other isolates clustered with strains from South Korea, Germany, and Japan. Notably, the Iran-5 group exhibited high similarity to a non-typeable strain from the United States. Additionally, eight isolates were found to harbor truncated hagA proteins, each consisting of one amino acid fewer than the full-length protein, which comprises 345 amino acids. This study indicates the circulation of diverse genotypic groups of Av. paragallinarum strains in Iran. These findings highlight the need for further molecular investigations to improve control measures and assess the efficacy of the vaccines currently used in the country.