Background: Infectious pancreatic necrosis virus (IPNV), a member of the virus family Birnaviridae, causes an acute, contagious disease with high mortality rate in a number of economically important fi sh species specially salmonids. During April 2009, one Rainbow trout farm, situated in Gilan province, north of Iran, reported unusually high losses of reared rainbow trout fry with average weight of 560 mg. same mortality were reported from 4 other farms in fryes under 1 gram weight in 2010. Clinical signs included darkening, exophthalmia, distended abdomen, fecal cast and a spiral swimming motion. Cumulative mortalities were more than 90%. Water temperature was between 12 to 16°C. Alive affected fi sh were delivered to the virology laboratory of Inland water aquaculture institute situated in Bandar anzali for diagnostic investigation. Clinical signs, mortality levels, age and size of fi sh and necropsy fi ndings suggested that IPNV might be present. The presence of virus was confi rmed by virology methods with cooperation of community reference laboratory of fi sh disease, Arhus,Denmark. Methods and Materials: Pools of viscera from each fi ve whole fry were homogenized, re-suspended in medium and clarifi ed by centrifugation at 2000 rpm for 20 minutes in 4°C. Supernatants were inoculated onto monolayers of the BF-2 and EPC cell lines in 24 well multidishes and identifi ed by ELISA, IFAT, NT, Nested-RT-PCR and Chloroform test. The PCR product of an isolate was sequenced and the Phylogenic tree was constructed from the sequencing data. Results: CPE was observed 24h post inoculation and IPNV identifi ed by ELISA, IFAT, Nested-RT-PCR and Chloroform test. In neutralization test, the virus showed more closely relationship to the SP (A2) serotype. Through an analysis including to other polyprotein gene sequences deposited in Genbank, a Spanish isolate ( ATCC AJ489222.1) was found more similar to Iranian isolate. Conclusion: Serotype of aquabirnavirus isolated in this study suggesting that the original source of the virus was in Europe. This is the fi rst isolation and identifi cation of IPN virus from rainbow trout fry in Iran.