An outbreak of fever and dyspnea with high incidence rate and case fatality rate occurred among pigs in a pigfarm in Jilin province, China, in 2000. The paramyxovirus-like particles could be observed in lungs, spleens and kidneys of the dead pigs under the transmission electron microscope. A Newcastle disease virus (NDV) isolate designated as JL01 was determined as the causal agent for the disease outbreak. The purified virus was reinoculated into pigs, and then the pigs infected with the virus showed similar symptoms, and the HI antibody of NDV could be detected from the reinoculated pigs. The MDT, ICPI and EID50 of the JL01 isolate was 55.2h, 1.60 and 10(-7.5)/0.1 mL respectively. The F gene of JL01 was cloned and sequenced, and the results showed that the identities of F gene shared by JL01 and avirulent NDV reference strains were from 91.5% to 98.5%, and could be ascribed to NDV genotype I. Thus, the swine NDV JL01 strain should be an avirulent strain with gene variation, but the virulence of JL01 was just the same as velogenic strains.