Background:The entire effects of different bleaching regimens on the mechanical properties of composite resins have remained unknown. The purpose of this study was to evaluate the effects of different bleaching regimens on the flexural strength (FS) of hybrid composite resins.Materials and Methods:In this in vitro study, 80 bar-shaped specimens of hybrid composite resins were fabricated and randomly divided into four groups, 20 specimens in each group. First group (C) was considered as control. The other groups were treated by home bleaching (HB) agent, in-office bleaching (IB) agent, and the combination regimens (HIB), respectively. The FS was evaluated by three-point bending test by using a Universal Testing Machine. All data were analyzed by using Statistical Package for the Social Sciences (SPSS) software version 18, analysis of variance (ANOVA), and Turkey's post hoc statistical tests (α = 0.05).Results:The maximum mean value of FS was seen in HB group with significant differences to other groups (P < 0.05). Also, the minimum FS was observed in group HIB.Conclusion:Application of different bleaching regimens does not have any adverse effect on the FS of hybrid composite resins. However, the administration of HB regimens seemed to have lesser negative impact on the FS.