Abstract: To identify if there was the mechanism of active efflux in erythromycin resistant Streptococcus strains with mefA gene isolated from veterinary clinic，several erythromycin resistant strains with mefA gene, ermB gene and several susceptible strains were selected in this test. The uptake of 14C-erythromycin in all strains and the effects of carbonylcyanidem chlorophenylhydrazone (CCCP, a proton conductor,) on the erythromycin accumulation were assayed with intact cells. The results showed that increased active exocytosis and decreased accumulation of erythromycin (P<0.05) were occurred in strains with mefA gene, and CCCP led reverse results. The accumulation and the response to the addition of a proton conductor indicated that the erythromycin resistant strains with mefA gene could actively pump out 14C-erythromycin from the cell.