Dietary acids are known to be one of the most common causes of enamel erosion. While previous studies found that lasers have the potential to increase enamel resistance to acids, the period of protection against enamel erosion have not been fully investigated. Objectives: The aim of the study was to evaluate the potential preventive effect of Er: YAG laser in-vitro on enamel erosion when exposed to an acidic beverage over a period of time. Methods: Five human molar teeth were lased with Er:YAG laser at energy density 5100 mJ/cm2 with water cooling. These lased teeth were sectioned with a hard-tissue microtome to obtain twenty enamel sections with mean thickness of 120µm. The sections were covered with clear acid resistant varnish on all surfaces leaving the natural surface exposed for conditioning in Coca-Cola® (pH 2.5) at 37°C, constantly stirred at 120 rpm, for a period of 5 hours. The sections were characterized under polarized light microscopy at the end of every hour. Images of the erosive lesions were digitally analyzed and measured. Results: The results showed that the mean depth of erosive lesion over the lased areas increased from 36.55±24.23µm (s.d.) to 121.76±39.48µm (s.d.) from 1 hour to 5 hours, respectively. The mean depth of erosion for unlased areas was deeper and ranged from 51.71±35.64µm (s.d.) to 130.21±41.02µm (s.d.) from 1 hour to 5 hours, respectively. The deeper depth of erosion seen in unlased over lased areas was statistically significant (p<0.05) for the period of 1 to 4 hours. Conclusion: This in-vitro study showed that Er:YAG laser has the potential to reduce enamel erosion to acidic beverages for a period of 4 hours. This study was supported by NUS ARF R-222-000-014-112.