The aim of this study was to evaluate microleakage of composite restorations submitted to marginal treatment. Class V preparations with walls located in enamel were performed at buccal and lingual surfaces of eighteen recently extracted, non-carious human premolars. Cavities were restored with composite resins and adhesive system. Samples were stored in distilled water for 48h and polished with Sof-Lex discs. Teeth were randomly divide in six groups: G1 - Control; G2 - marginal treatment with surface sealant; G3 - Nd:YAG 25 Hz, 80mJ, 2W; G4 - Nd:YAG 20Hz, 100mJ, 2W; G5 - Nd:YAG 30Hz, 60mJ, 1.8W; G6 - Nd:YAG 30Hz, 40mJ, 1.2W. Contact fiberoptic (300μm) pulsed (1.064 μm) Nd:YAG laser was used for 30sec, under air cooling. Teeth were impermeabilized, immersed in a dye (Rhodamine B) for 4h at 37°, and sectioned. Specimens were evaluated under light microscopy and evaluated with scores. Results were analyzed with Kruskal- Wallis test (p=0.05) and showed that there were significant differences between marginal treatments; there were no significant differences beaten groups 1, 2, 4 and 3, 5, 6; lower values of microleakage were at groups 3, 5, 6. Nd:YAG laser showed marginal sealing ability and decreased microleakage of composite resins restorations.