Abstract: Objective The objective of this study was To investigate the function of luxS gene in iron metabolism of Streptococcus mutans. Methods The absorbance of standard strains and deficient strains of Streptococcus mutans cultured in the iron-limited defined medium for 24 hours was measured and analyzed. exogenous iron or the supernatant fluid of standard strains was added into iron-limited defined medium of deficient strains of luxS gene mutant, and the A value was further measured and analyzed. Results After incubation for 24 hours, the growth of both standard and luxS gene mutant strains in medium containing 0.1 mmol/L of 2,2′-bipyridyl was not significantly inhibited. However, the growth of luxS gene mutant strains in medium containing 0.3 mmol/L and 0.5 mmol/L of 2,2′-bipyridyl was significantly inhibited. The growth inhibition of luxS gene mutant strains in medium containing 0.3 mmol/L of 2,2′-bipyridyl was relieved by adding exogenous iron and culture supernatant of standard strain into the medium, so was it when the luxS gene mutant strains were tranferred into fresh medium, and the growth of luxS gene mutant strains could get relatively high cell concentrations. Conclusions luxS gene plays a role in iron metabolism, and it may regulate the growth of Streptococcus mutans to a certain degree in iron-limited medium via AI-2.