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The objectives of this study were to compare the microhardness, flexural strength and compressive strength of a new bulk-fill composite (SonicFill™) to a conventional nanohybrid composite (Herculite Precis) and an established bulk-fill composite (Tetric N Ceram). In addition, the depth of cure of the two bulk-fill resin composites was also investigated. The materials were prepared and tested for the mechanical properties following ISO 4049:2009. Microhardness and depth of cure were measured using Vickers hardness tester. Compressive and flexural strength were tested using a universal testing machine. To determine the depth of cure, microhardness of the bulk-fill composites were measured as a function of selected depth of materials at 0.5 mm, 2.0 mm and 4.0 mm. Data were analyzed by either one-way ANOVA or Friedman test. Analysis demonstrated that SonicFill™ gave the highest microhardness value (101.8 + 4.6 VHN) compared to the other two groups. There were no significant differences among all groups in flexural and compressive strength. The depth of cure decreased as the thickness of both bulk-fill composites increased. In conclusion, SonicFill™ showed favorable mechanical properties compared to other composites tested. In both bulk-filled groups, microhardness value decreased as the thickness of the composite increased. The polymerization of the bulk-filled composites was effective only at 2 mm or less.