Objective To compare the production of organic acid of different genotype Streptococcus mutans（S. mutans） isolated from children with different caries experience. Methods 66 strains of S.mutans isolated from dental plaques of children aged from 3 to 5 with different caries experience were chosen as test bacteria. The quantities of organic acid include formic acid, acetic acid and lactic acid which produced by different genotype of S.mutans, were measured by gas chromatograph. Results There were significant difference in production of organic acid among the different genotypes of S.mutans isolated from children with different caries susceptibility, and so were the strains isolated from children within the same caries susceptibility（P
