Objective: To analyze in vitro the endogenous pH and the effect of industrialized fruit juices on the microhardness of permanent tooth enamel. Material and Method: Sample was composed of 10 beverages from two commercial brands and different flavors. Experimental groups were formed by selecting the beverages with lower and higher pHs according to the brands. Twenty-five specimens were prepared from human third molars and randomly assigned into five groups: G1: Ades Uva®, G2: Ades Morango®, G3: Kapo Uva®, G4: Kapo Laranja® and G5: Control (distilled water). Vickers microhardness was analyzed before (T1) and after (T2) the demineralization-remineralization cycles by applying a 100 g load during 15 seconds. The specimens were immersed in the juices during 1 minute, followed by 3 minutes in artificial saliva. Wilcoxon test was used for statistical analysis with 5%significance level and 95% confidence level. Results: All beverages presented pH values below the critical value of 5.5 for enamel demineralization, varying from 3.53 to 3.93. Microhardness analysis showed statistically significant difference (p=0.04) in all experimental groups, the largest reduction was observed in G1 (190.67). Conclusion: All beverages promoted a significant decrease in permanent enamel microhardness, being considered as potentially erosive under the conditions of this study. DESCRIPTORS Hardness Tests. Dental Enamel. Fruit Juices.