Objective: The aim of this study was to investigate the effect of various acidic fruits on surface hardness of human enamel. Methods: Green mango (Anacardiaceae Mangifera indica) and pineapple (Bromeliaceac Ananas comosus), Tangerine (Citrus reticulata Blanco) juice were prepared by juicer machine. These solutions were used as experimental conditions whereas citrate buffer pH 5 and 0.9% of NSS are as comparator and control, respectively. The pH of solution was measured by pH meter (ORION 520A). Human third molar teeth were used. Five specimens of each group were immersed in prepared solution for 30 minutes at 37°C. After immersion, all specimens were rinsed for 1 minute with distilled water and then transferred to NSS for 60 minutes. Specimens were exposed cyclically to storage solution for 7 times. Fresh juice was replaced at each cycle. Surface hardness was measured prior and after exposure using Microhardness tester (Micromet II Buehler) at each time interval. Specimens were prepared in a similar process for scanning electron microscopy. Hardness values were analyzed using ANOVA with repeated measurement. Result: pH of green mango, pineapple and tangerine juice were 2.6, 3.9 and 4.4 respectively. All specimens immersed in storage solution showed decrease in surface hardness. The greatest reduction of surface hardness was occurred in the group exposed to green mango juice. Pineapple and tangerine juices produced similar hardness reduction to there observed with citrate buffer pH 5. SEM presented etching pattern after immersed in all storage media at various time intervals. Conclusion: The pH of three types of sour fruit juices was lower than critical pH (pH 5.5) of demineralization. Immersion of teeth in mango, pineapple, tangerine juice and citrate buffer showed a reduction in surface hardness and produce the etching pattern of enamel. These results show the erosive potential of these sour fruit to enamel.