Objective: To examine the effect of polymerization on color stability of five different resin cements. Materials and Methods: A silicon mold was used to prepare 50 cement resin annuli (2 mm thick and 18mm diameter with a central hole of 8 mm) of five groups (n=10). Group A: Smart Cem 2 resin cement; Group B: RelyX U200 resin cement; Group C: RelyX Ultimate resin cement; Group D: Calibera Esthetic veneer resin cement; Group E: RelyX Veneer resin cement. Colorimetric values of the specimens before and after polymerization were measured using a spectrophotometer. The CIE L*a*b color system was used for the determination of color difference. Kruskal-Wallis test was used to analyze the data for significant differences. (P≥0.05). Results: There were noticeable color changes in all groups (ΔE*ab ≥ 3.3). Group C (RelyX Ultimate) showed the highest color change (6.66±0.24) while Group D (Calibera Esthetic veneer) had the lowest color change (3.78±0.18). Kruskal-Wallis test reveled high significant difference between four tested groups p<0.05. Conclusions: Tested resin cements showed color changes above the clinically accepted value in all study groups (ΔE*ab≥3.3). Key Words: Resin Cement, Color Stability, Spectrophotometer, and ΔE.