〔Abstract〕 In order to study the inhibition effect of MTAN(a mixture of Nisin, acid, and detergent)and MTAN+(ethylene diamine tetraacetic acid, EDTA)onS.sanguinis,F.nucleatumandP.gingivalispaired mixed bacteria solutions and three-in-one mixed bacteria solution, MTAN and MTAN+EDTA with different Nisin concentrations were used to treatS.sanguinis,F.nucleatumandP.gingivalispaired mixed bacteria solutions and three-in-one mixed bacteria solution respectively, and the OD method was adopted to measure MIC and MBC. The results showed that MTAN had inhibitory effect on all mixed bacteria solutions. With the increase of concentration, the inhibitory effect was enhanced. When Nisin concentration was ≥250 μg/ml, bacteria could be killed. MTAN+EDTA with different concentrations of Nisin inhibited all mixed bacterial solutions, and when the concentration of Nisin≥2.5 μg/ml, bacteria could be killed. Therefore after MTAN acts on all the mixed bacteria solutions, it has obvious bacteriostatic effect, and this effect is obviously improved with the addition of EDTA.