Abstract: Objective The pathogenic strain to result in measles epidemic in Shanxi province was identified,to search for factors concerning measles vaccination.Methods Samples of thro at swabs from measles patients were collected forisolation of measles virus;to obtain RNA from measles virus suspensions by the phenol-chlorofor mextraction method,to amplify 450 nucleotide seg ments(bp)at carbon-terminal of N-gene by reverse transcription polymerase-linked reaction(RT-PCR),and to identify the sequence and genotype of the amplified segments.The neutralization(NT)antibo dylevels for measles vaccine virus and for wild measles virus in sera from healthy people and acute measles patients were determined by trace neutralization test.Results A total of 82 samples of throat swabs were collected,with 19 strains of positive measles virus isolated,these strains were H1 genotype of measles virus.The anti-wild type measles virus NT antibody geometric mean titer(GMT)in the serum of vaccines and naturally infected individuals with the history of immunization were 26.36 and 26.90 respectively).which was obviously lower than anti-measles vaccine strain(GMT was 49.30 and 56.18 respectively).Conclusion Measles epidemics in Shanxi province recent years were resulted by H1 genotype measles virus,possibly partly because measles vaccine cannot induce adequate protective level to current epidemic strain.