Objectives: This study is intended to evaluate the effect of a ‘novel' sonic-driven resin composite application device on the microleakage pattern of a bulk-fill resin composite Materials and Methods:    Standardized Class V cavities in 60 sound extracted human molars were prepared. Three different placement techniques were used for the application of the bulk-fill resin composite. Microleakage test was evaluated by dye penetration using a coaxial stereo-microscope. Results: There was no significant differences (p >0.05) between the tested groupsregarding the technique of application either before or after thermal cycling. Conclusion: the new application technique does not seem totally improve the microleakge of the bulk-fill resin composite. Keywords: compothixo, sonic vibration, Microleakage Class V restorations, bulk-fill..