Abstract: Objective: To compare the microleakage of composite resin restorations using a sonicfill system and a layered filling technology. Methords: Class-Ⅱcavities (3 mm×4 mm×5 mm) were prepared on 20 freshly extracted molar teeth. The teeth were randomly divided into 2 groups with 10 teeth each. Group A was restored with Sonicfill system. Group B was restored with the traditional way. After restoration, all teeth were stained with 2% methylene blue solution for 1 week. The depth of methylene penetration was measured under the scanning electron microscope. Results: There were no significant differences between group A and B. Conclusions: The new Sonicfill system was the same as the traditional layered filling technology in the microleakage of composite resin restoration.