Objective: Eating pattern of local acidic diet among Thai population may have the effect on tooth surface. The aim of the study was to investigate this effect on surface hardness of enamel over a period of time. Method: Four storage media were used in this study: Kangsom (spicy and sour soup), Somtum (papaya salad), Yummamuong (green mango salad) and citrate buffer pH 5.0 whereas distilled water used as a control. These solutions of erosive food were prepared using a blender machine. After blending, solutions were sifted through cloth filters. The pH of solutions were examined by pH meter (ORION 520A). Sixty three human molar teeth (embedded in epoxy resin) were ground to obtain a flat occlusal surface. Specimens were immersed cyclically to storage media for seven rounds. Surface hardness was measured by microhardness tester (Micromet II) at each time interval. Hardness data were analyzed using ANOVA and multiple comparison test. Specimens were processed for scanning electron microscopy. Result: The pH of Kangsom, Somtum and Yummamuong were 4.6, 4.5 and 3.9 respectively. The surface hardness measurement (kg/mm2) demonstrated that the distilled water did not produce effect on surface hardness value but the acidic storage media had shown decrease in surface hardness in varying degree over the test period. The surface hardness of enamel exposed to various storage media (Yummamuong, 57.5±10.9; Kangsom, 198.3±3.6; Somtum, 181.4±6.7 and citrate buffer solution, 76.9±5.6) decreased statistically significant (p<0.05) when compared with distilled water (278.2±3.4). Conclusion: Some local Thai food are acidic which pH are lower than critical pH (pH 5.5). This could affect on enamel surface. Acidic food produced the enamel surface changed in various degrees. Furthermore, the frequency of exposure has provided influence on erosive potential to enamel surface.