Objectives: This research was designed to evaluate the effect of polymerization shrinkage of different bulk-fill resin composites. Materials & Methods: Ninety extracted molars were prepared as specimens by having a box shape proximal cavity for the restoration of composite resins. The specimens were divided into three main groups (n=30), according to the resin composite materials used (sonic fill, flowable and packable bulk-fill). Profile projector was used for assessment of polymerization shrinkage Results: There is no significant difference between the variables. Sonic fill composite resin has lower polymerization shrinkage than flowable bulk-fill composite and packable bulk-fill composite. The marginal adaptation of sonically activated resin composite is more than the polymerization shrinkage of sonically activated resin composite, while the storage time of sonically activated resin composite is less in bulk-fill .Conclusions: Success of resin composites depends primarily on the degree of polymerization shrinkage as when the shrinkage decrease mostly the post-operative problems decrease.