Objectives: Cervical carious lesions account for about 20% of permanent tooth decay. These class V cavities are mostly filled with tooth colored restorations. Microleakage is an important problem with tooth colored restorations. Some studies show that ultrasonic scalers could cause microleakage. The aim of this study was to examine the effects of ultrasonic scaling on 3 different tooth colored restorations namely composite resin, glass- ionomer and comboglass. Methods: 60 extracted premolars were randomly divided into 3 groups of 20 teeth each. In all teeth the same size class V cavity was prepared. First, second and third group teeth were filled with composite, gloss inomer and compoglass respectively. After thermocycling, half of the teeth in each group were scaled with ultrasonic (test group) whereas, the other half was used as control. Then all the specimens were kept in 2% fushion for dye penetration testing about 24 hours. After sectioning, the specimens' microleakage was quantified with electronmicroscope. Results: In the first (composite) and the third (comboglass) groups ultrasonic scaling had no effect on microleakage whereas, in the second group (glass-ionomer) ultrasonic scaling caused more microleakage than in the control group. The difference was statistically significant. Conclusion: The ultrasonic scaler should be used with caution around class V cavities filled with tooth colored restorations, due to the possible microleakage effect.