Aim: The aim of this study was to assess the effectiveness of composite cure of many newly introduced bulk-fill composites Materials and methods: Five types of dental composite materials of A2 shade were selected for this study. Three packable bulk-fill composites: Tetric N Ceram (Ivoclar Vivadent), Filtek bulk-fill posterior composite (3M ESPE) and X-trafill bulk-fill packable composite (VOCO) and two conventional composites: Quadrant Universal L.C Composites (CAVEX) and Composan Bio-esthetic Nano-ceram Composite (PROMEDICA). Ten specimens were prepared from each type of composite material, each composite specimen was prepared by compressing sufficient amount of composite into a mold (6 mm in diameter and 4 mm in thickness) for bulk-fill composites and (6 mm in diameter and 2 mm in thickness) for conventional composites. The total fifty composite specimens (n = 50) were cured for 20 seconds from the top surface only with Woodpecker LED light curing unit by making the curing tip in intimate contact with the acetate celluloid strips covering the composite surface. After that, the composite specimens were incubated in distilled water at 37° C for 24 hours. Then the 50 composite specimens were tested with Vickers microhardness tester (Microhardness tester FM-800, FUTURE-TEC H, Japan) at 300 g load and 15 seconds according to ISO 4049 for both top and bottom surfaces by making three indentations of both surfaces and considering the mean microhardness value for each surface. The hardness ratio of each specimen was calculated by using the formula (HR {Mean Vicker's hardness of the bottom/Mean Vicker's hardness of the top} x 100). Data were statistically analyzed using mean, standard deviation, one way Analysis of variance (ANOVA) and T-test at 5% level of significance. Results: Statistical analysis of the data revealed, there was a significant difference between the five groups being tested (ANOVA, p ≤0.05). The material with the highest hardness ratio was Cavex followed by X-trafill, Composan, Filtek bulk-fill packable and Tetric N ceram which did not achieve adequate curing (80% hardness ratio). Conclusion: Composite formulation in general significantly affects the effectiveness of composite cure. Clinical significance: Inadequate curing of composite might be considered one of the main causes behind composite restoration failure by negatively affecting its physical and mechanical properties including solubility, bonding qualities and more residual monomers production that are considered highly toxic to pulpal tissue. All these problems can be avoided clinically by former assessment the effectiveness of curing related to that specific composite material being selected.