Aim: This research was designed to evaluate the flexural strength and depth of cure of Sonic Fill resin composite at different storage times. Materials and methods: Two Bulk-fill composites (Sonic fill, kerr; X-tra fill, Voco) and one incremental-fill composite (Herculite XRV, kerr) were used. For Flexural strength (FS) 45 Bar-shape specimens have created through mini flexural mold with specific diameters has: (2mm width ×2mm depth×12mm length) Using Teflon molds. The mold was filled with all resin composites material. FS was determined using the three-point bending test in a universal testing machine. For depth of cure (DOC) a 90 human molars, free from caries, extracted for pathologic reasons were collected to be used in this study. Standardized box-shaped cavity preparations were prepared on both proximal surfaces of each tooth with cavity depth of 2 and 5mm. Specimens were stored in artificial saliva in dark at body temperature (37±1) for one day, one month and three months before testing. (DOC) was determined using the Vicker's microhardness test for one half of the specimens on top and bottom surfaces of each specimen. Data for FS and DOC were analyzed by ANOVA and pair-wise Newmanekeuls test. Results: It was found that the highest mean value of FS was recorded for sonic fill composite group at one month storage time, while the lowest mean value was recorded for Herculite XRV composite group at three months as indicated by two way ANOVA test. Pair-wise Tukey's post-hoc test showed no-significant between one month and three month storage. Also it was found that DOC mean values of X-tra fil composite group recorded statistically significant highest B/T ratio mean values at one month storage time followed by sonic fill composite group at one month, while the lowest statistically significant B/T ratio mean Values were recorded for Herculite XRV composite group at three months, as indicated by two way ANOVA tests. Pair-wise Tukey's post-hoc test showed no-significant between one day and three months storage time subgroups. Conclusion: It can be concluded that sonic full composite with special designed unique activated - system (hand-piece with unidose - tip) is considered better bulk -fill composite material that used in posterior restoration. Differences in FS and DOC values among materials proved to be a material dependent.