The study, using sequence analysis and the phylogenetic relationship of the fusion protein gene, divided the Korean epizootic isolates of Newcastle disease virus (NDV) into several lineages to determine the molecular epidemiology of the virus. A 695 base pair fragment was amplified by polymerase chain reaction between matrix protein gene and fusion protein gene of 30 Korean NDV isolates, which were isolated from field outbreaks of Newcastle disease between 1949 and 2002. All isolates showed the amino acid sequence 112R-R-Q/R-K-R116 at the C-terminus of the F2 protein and phenylalanine (F) at the N-terminus of the F1 protein, residue 117. These amino acid sequences were identical to a known virulent motif. The region of the F gene between nucleotides 47 and 435 was compared by phylogenetic analysis. Based on nucleotide sequence, the Korean NDV isolates belonged to genotype III, V, VI and VII corresponding to isolates in 1949, 1982 to 1984, 1988 to 1997, and 1995 to 2002, respectively. These data showed that genotypes of five Korean Newcastle disease epizootics had replaced each other serially (III, V, VI and VII) in chronological order. Further, the five Korean Newcastle disease epizootics were closely related with the Newcastle disease panzootics or Newcastle disease epizootics in other countries. Present study showed that the Korean genotype V isolated before 1984 was related with European Newcastle disease epizootics in the 1970s, whereas the Korean genotypes VI and VII isolated after 1988 were more closely related with Far East Newcastle disease epizootics, especially Newcastle disease epizootics in Japan, Taiwan and China. Since 1988, the genotypes VI and VII of Far East origin were dominant in South Korea. That might be due to the increased trade of agricultural products including poultry among Far East Asian countries.