OBJECTIVE: To evaluate the capability of quantitative light-induced fluorescence (QLF) for monitoring the remineralization of lesions lengthways and distinguishing the effect of different fluorides. METHODS: Following baseline early caries examination, 305 school students (age from 11 to 14 years old)were qualified from Chengdu area. The schools in which the subjects studied were randomized into three groups: NaF group, MFP group and nonfluoride group. The subjects of three groups brushed the teeth with 1450 mg/L sodium fluoride dentifrice, 1450 mg/L sodium monofluorophosphate dentifrice and non-fluoride dentifrice, respectively. QLF images of early lesions on smooth surfaces of the maxillary anterior teeth were taken at baseline, three and six months after the initiation of experiment. These images were analyzed by the trained examiner with the area of lesion (Area), fluorescence loss (deltaF) and gross fluorescence loss quantity (deltaQ). RESULTS: 296 school students completed the study. After three months, the lesions on smooth surfaces got better in all three groups. The change of Area, deltaF and lg deltaQ amongst three groups had no statistical significance (P>0.05). After six months, the lesions on smooth surfaces also got better in all three groups than at baseline. The change of Area, deltaF and lg deltaQ of the lesions in NaF group and MFP group exhibited significant decreases than that of no-fluoride dentifrice group (P0.05). CONCLUSION: As a diagnostic method which could quantify the miner content, QLF system has the capability of monitoring the variations of lesions lengthways.