Since the effect of calcium carbonate (CaCO3) based dentifrice on enamel demineralization is not clearly established, it was evaluated using the IEDT model described by Zero’s group in 1992. This study had a crossover design and 10 volunteers were submitted to 3 treatment groups: a negative control, brushing without dentifrice; an active control, brushing with silica-based dentifrice (SiO2/MFP group), and the experimental group, brushing with CaCO3-based dentifrice (CaCO3/MFP). Both dentifrices contained 1,500 µg F/g (w/w) as sodium monofluorophosphate (MFP). Enamel surface microhardness was determined in the dental blocks and the percentage change in relation to baseline was calculated. Fluoride uptake in enamel and its concentration in ‘test plaque’ were determined. The results showed that the dentifrice containing CaCO3/MFP was more effective than SiO2/MFP in reducing enamel demineralization (p < 0.05). A higher concentration of fluoride ion was found in ‘test plaque’ treated with CaCO3/MFP than in the negative control (p < 0.05). The results suggest that CaCO3 abrasive may enhance the effect of fluoride present in dentifrice on dental caries control.