This study aimed to evaluate the effect in vitro of a single application of a stannous fluoride- (SnF2-) containing toothpaste on eroded enamel. Forty-eight teeth were subjected to three acid treatments: 15% hydrochloric acid for 120 s (HA group); 1% citric acid (pH=4) for 180 s (CA group); 37% phosphoric acid for 30 s (PA group). They were brushed with an electric toothbrush with pressure control and 1 g of SnF2 (1100 ppm) toothpaste for 2 min. Polyether replicas of buccal enamel surfaces were obtained at baseline, after acid exposure and after brushing, gold sputtered and inspected by SEM for fluid droplets presence. Hydrochloric and citric acid treatments increased enamel permeability while, on the contrary, phosphoric acid reduced enamel fluid release. SnF2 application of ameliorated acid induced permeability in citric and hydrochloric treated samples. Permeability in phosphoric treated enamel was unchanged after topical application of SnF2. Our data show specific acid-dependent effects on enamel permeability and demonstrate that SnF2 application can reverse acid-induced permeability.