Viral haemorrhagic septicaemia (VHS), caused by the rhabdovirus VHSV, is the most economically important viral disease in the world rainbow trout farming. In recent years suspected cases of this disease have been observed in Iran rainbow trout farms. To evaluate the outbreak and genetic diversity of VHSV, sampling was performed from the 11 provinces (33 farms) in North, South West, West and center of Iran. Positive samples were determined using RT-PCR method and amplification of the partial nucleoprotein (N) gene (505 bp). In the next step amplified gene fragments were sequenced and eventually used to build phylogenetic tree. These sequences were analyzed to evaluate their genetic relationship with 128 isolates from Genbank, representing the four known genogroups of VHSV. The prevalence of disease in the sampling farms was 21/21%. The results showed sequence variation in three codon positions, one mutation was missense and two were silent. Phylogenetic analysis by nucleotide sequences showed that all the VHSV isolates in this study were closest related to the fresh water strains from Denmark and Germany and grouped in genotype I sublineage Ia. This finding indicates that Iranian VHSV isolates have a European origin. Keywords : Viral hemorrhagic septicemia, Rainbow trout, Genetic diversity, RT-PCR, Iran.