Purpose: To evaluate interface degradation leading to marginal microleakeage in Class II restorations that had received an application of surface sealant at the tooth/restoration interface or not. Materials and Methods: Eighty bovine incisors were used, and the teeth were split obliquely, 10 mm from the amelodentinal proximal junction, and finished with water abrasive papers to obtain a smooth, flat incisal surface. Cavities were made to simulate Class II preparations (8 mm high, 4 mm wide and 1.5 mm deep), and the restorations were performed with a composite resin. Teeth were then randomly allocated into 8 groups according to the surface sealant (none, Fortify, Single Bond 2, or Scothbond MP Plus) and aging process (none or thermocycling and storage for 6 months). Microleakage was then evaluated using a dye penetration method immediately after the restoration or after aging. The samples were triturated and assessed by spectrophotometer. Results: Microleakage was statistically similar in all groups when assessed immediately after the restorative procedure. After aging, teeth sealed with Fortify presented better results than the other groups. Conclusion: Aging causes interface degradation and increased microleakage. Surface sealant can reduce these effects and decrease microleakage in Class II restorations. Keywords: composite resin, surface sealants, microleakage, degradation