Abstract:The genetic polymorphisms of partial sequence of OSTF1（osteoclast stimulating factor 1）gene in 227 Holstein cows were detected by PCR-SSCP with five pairs of primers P1-P5.Two polymorphic sites,A45416G and C45436T of primer P3 were found,and A45416G mutation caused amino acid change (methionine→valine).Five genotypes (AA,AB,BB,AC and CC) were found in Holstein cows,and the genotype frequencies of AA,AB,BB,AC and CC were 0.515,0.366,0.075,0.035 and 0.009,respectively.The relationship between polymorphisms of OSTF1 gene and somatic cell score (SCS) in Holstein cows was analyzed by least squares linear model.Least squares mean of SCS for BB genotype was significantly lower than that for AA,AB or AC (P<0.05),and no significant difference was found in least squares mean of SCS between other genotypes (P>0.05).So genotype BB was mastitis resistant and it may be used as a molecular genetic marker to improve the phenotype of anti-mastitis in Chinese Holstein dairy cows.