This study evaluated the vitro performance of the effect of in-office bleaching (Zoom gel material) on the color changes of the one hundred twenty discs specimens, 5 mm in diameter and 2 mm thickness and shade color (A1). these were divided to three groups according to material which prepared from; Beautifil II (B), ISP Empress Direct (E) and Ceram.x.mono composite resins (C), each group's discs specimens were subdivided into four subgroups (n=10), according to the time follow up. All specimens’ discs were polished and stored in distilled water at 37°C for one week. These specimens' discs were exposed later to four sessions of in office bleaching. The colorimetric measurements were performed at baseline (before bleaching), 48 hours after bleaching, 3 months and 6 months after bleaching. Data statistically analyzed. Results showed: there were significant effects on the different color parameters L*, a* and b* according to the CIE L* a* b* color system and color change (ΔE) on the specimens of the three contemporary composite resins materials. Keywords: Restorative composite color changes, in-office bleaching gel, CIE L* a* b* color system, Beautifil II composite resins, ISP Empress Direct composite resins and Ceram.x.mono composite resins.