BACKGROUND: Newcastle disease virus (NDV) majorly infects the poultry, and despite high rates of vaccination, it is still circulating in different geographical regions. Due to the high mortality rate, the economic loss of Newcastle disease (ND) is enormous. OBJECTIVES: The molecular characterization of NDV isolates from chicken farms in Northern Iran, during 2017-2018, was the main goal of this study. METHODS: We isolated and characterized five NDVs from commercial broiler and backyard chicken farms during severe disease outbreak. The partial coding sequence of fusion (F) genes of isolates was determined and compared with those of other published NDVs. RESULTS: Phylogenetic analysis revealed that all of the isolates were grouped into sub-genotype VII.1.1 (formerly known as VIIl). All isolates carried multi‐basic amino acid residues at the cleavage site of fusion protein, typical of virulent strains. Studied NDV isolates had high homology with the prevalent genotype NDV strains that currently circulate in China and Republic of Korea (96.94%). CONCLUSIONS: Our results suggested that NDV sub-genotype VII.1.1 (VIIl), circulating among chicken farms, may be a dominant sub-genotype. Considering the genetic variation between the used vaccine strains (B1, LaSota, and Clone 30, all belonging to genotype II) and circulating NDVs, it is recommended that a contemporary homologous virus should be developed as the vaccine strain to avert the outbreaks of genotype VII viruses.