Objective To evaluate the effect of erythritol on cell wall structure of Streptococcus mutans(S.mutans) and explore its potential mechanism. Methods Enzyme activities of lactate dehydrogenase(LDH) in bacterial solution were detected under respective condition of sucrose and erythritol. A scanning electron microscope(SEM) was used to investigate the change of S.mutans’cell wall under the condition of sucrose and erythritol. Results Enzyme activities of LDH in erythritol culture medium were different from that in sucrose, but the difference was slight. SEM observation showed the integrity of cell wall was not destroyed and no content leaked out. Conclusion It’s suggested that erythritol has an antibacterial effect on S.mutans through no affecting on the normal structure of the cell wall of S.mutans.