Objectives: The aim of this study was to determine the effect of light curing time on top to bottom microhardness of bulk-fill resin composites. Materials and Method: Three bulk-fill resin composites were used Admira fusion x-tra (voco), Tetric Evoceram bulk-fill (Ivoclar vivadent) and Filtek bulk-fill (3M ESPE). Sixty composite specimens were prepared in cylindrical shape. Teflon molds (4mm×4mm) diameter that are open at the top and the bottom sides were used to prepare the specimens. Thirty specimens were cured according to manufacturers' instructions and the other thirty were cured for 40 seconds using EliparTM light curing unit. All the specimens were cured at 0 mm distance. After curing process, the specimens were stored at 37˚C at 100% humidity for 24 hours. Surface microhardness was measured and data presented as means and standard deviations (SD). Multivariant ANOVA was used to study the effect of different curing time on top and bottom values of microhardness. One-way ANOVA was also used to study the effect of different curing time on top/bottom ratio of microhardness. Results: Curing time showed a non-statistically significant effect on top and bottom mean values of microhardness of bulk-fill composite at P > 0.05. However, curing time showed a statistically significant increase on top to bottom microhardness mean ratio of all the materials P ≤0.05. Conclusion: Under the limitations of this study, it can be concluded that, the increase in the light curing time increased the top to bottom microhardness of bulk-fill materials.