Objective: The aim of the present study was to evaluate the effects of different surface pre-treatment techniques on the microleakage of a resin-based fissure sealant material. Methods:Thirty-five molars were divided into the following seven groups based on the surface pre-treatment technique used:(a) Erbium:Yttrium Aluminium Garnet (Er:YAG) laser (7 W); (b) Er:YAG laser (7 W)+acid etching (with 37% phosphoric acid); (c) Er:YAG laser (5.5 W); (d) Er:YAG laser (5.5 W)+acid etching; (e) air abrasion+acid etching; (f) air abrasion; and (g) conventional acid etching. The sealant was placed according to the manufacturers' instructions and light-cured for 20 sec. The sealed teeth were thermocycled for 10,000 cycles (58-55 degrees C), then immersed in 5% methylene blue for 24 h and sectioned mesiodistally. Each section was analyzed and photographed using a light microscope. Microleakage was assessed quantitatively by the degree of dye penetration and also qualitatively, scored on a three-point rating scale. Data were analyzed by one-way analysis of variance (ANOVA) and the Kruskal-Wallis test. The level of significance was set at p < 0.05. Results:Regardless of the fissure morphology and penetration depth, enamel surfaces conditioned with Er:YAG laser irradiation exhibited significantly higher microleakage than those conditioned with air abrasion followed by acid etching, and those conditioned with conventional acid etching (p < 0.05). Air abrasion followed by acid etching, as well as conventional acid etching, provided a sufficient seal, whereas laser irradiation alone or in combination with acid etching exhibited higher microleakage than did the other groups. Conclusions: Conventional acid etching remains the most effective and the simplest technique.