Abstract: To investigate the mechanisms of erythromycin-resisant streptococcus isolated from animals,the minimal inhibitory concentrations(MICs) of pencillin, erythromycin and clindamycin against streptococcus were detected by agar two-fold dilution, the resistance phenotypes of erythromycin-resistant streptococcus were determined by the double disk test, and the presence of mefA, ermB genes were determined by PCR amplification. The results showed that the rate of resistance to penicillin, erythromycin and clindamycin of 111 strains studied were 54.95％，68.47％and 64.86％,respectively. In 76 erythromycin resistant strains, 62 isolates (8158%) were assigned to the cMLS_B phenotype, 5 isolates (6.6%) were M phenotype and 9 isolates (11.84%) were inducibly resistant, expressing the iMLS_B phenotype by the double disk test. The mefA gene was present in all of the strains showing the M-resistance phenotype. Some isolates expressing a cMLS_B phenotype and iMLS_B phenotype were confirmed genotypically by the presence of the ermB gene, but 6 isolates were n’t detected the ermB and mefA gene. Genes coding for both resistance mechanisms were found in one strain. No amplification was detected in all the erythromycin susceptible streptococcus isolates. Erythromycin resistant Streptococcus isolated from animals mediated by ermB was predominant in China. The PCR amplification can be a useful method to rapidly screen the erythromycin resistant strains.