Abstract: In 1986 and 1987, rainbow trout eggs were imported from Japan. Soon after the importation, an acute infectious disease broke out in the hatched fry population at some fish farms in Shanxi Province. The disease cause a loss of 90%—95% of rainbow trout fry.A viral agent was isolated from rainbow trout. It produced cytopathic effect in some cell lines derived from salmonid. Infection studies showed infectivity of the virus 'o rainbow trout. The agent proved to be stable to chloroform treatment and resistant to heat and acid. Electron microscopy revealed icosahedral particles of 55—65 nm in diameter. The virus was neutralized with neutralized index(NI)of 5.0 by anti-IPN serum. Cross- neutralized tests suggest that the virus might be of Sp-serotype.According to the above results, the isolated agent is considered to be IPN virus. This was the first isolation of IPN virus in P. R. China.