objetives: the aim of this study was to verify the anticariogenic effect of acidulate solutions with low naf concentration, using ph-cycling model and bovine enamel. material and methods: enamel blocks were submitted to the surface microhardness (smh) test and randomly divided in 12 experimental and one placebo groups. the blocks were submitted to ph cycling for 7 days, with daily applications once/day of 0.05% naf and 0.1% naf and twice/day of 0.02% naf solutions. four different ph: 4.0, 5.0, 6.0 and 7.0 were used. next, smh test was again used to determine the surface microhardness percentage change (%smh). data obtained for %smh were homogeneous and passed through variance analyses and tukey's test (5%) as far as fluoride concentrations and ph. results:the results showed that ph influenced %smh in 0.02% naf and 0.05% naf solutions with ph 4.0, which had less mineral loss compared to ph 7.0 (p<0.05). the 0.02% naf - ph 4.0, and 0.05% naf - ph 7.0 groups showed similar results (p>0.05). a dose-response relationship was observed among the tested solutions, with better anticariogenic effect for the 0.1% naf solution. conclusion: the results suggest that the addition of citric acid to acidulate mouth rinses reduce mineral loss.