Objectives: The physical properties of dental restorative materials have a crucial effect on the longevity of restorations and moreover on the esthetic demands of patients, but they may be compromised by bleaching treatments. The purpose of this study was to evaluate the effects of in-office bleaching agents on the physical properties of three composite resin restorative materials. Method and Materials: The bleaching agents used were hydrogen peroxide and carbamide peroxide at high concentrations. Specimens of each material were prepared, cured, and polished. Measurements of color difference, microhardness, and surface roughness were recorded before and after bleaching and data were examined statistically by analysis of variance (ANOVA) and Tukey HSD post-hoc test at P .05. Results: The measurements showed that hue and chroma of silorane-based composite resin altered after the bleaching procedure (P .05). No statistically significant differences were found when testing the microhardness and surface roughness of composite resins tested (P > .05). Conclusion: The silorane-based composite resin tested showed some color alteration after bleaching procedures. The bleaching procedure did not alter the microhardness and the surface roughness of all composite resins tested. Keywords: bleaching, color, composite resin, microhardness, roughness, silorane