Objective: The aim of this study was to evaluate the effect of polymerization of three different resin cements, on the final color of two machinable ceramics milled using CAD/CAM.Material and methods: A total number of thirty ceramic discs were milled using CAD/CAM system. These were classified into two groups, according to type of ceramic material used.Group I: IPS empress CAD discs, and Group II: IPS e.max CAD discs. Each group was subdivided into three equal subgroups of 5 samples each. Subgroup A: Self-etch, self-adhesive resin cement (RelyX Unicem), Subgroup B: Light cured resin (Filtek Z350), Subgroup C: Dual cured resin cement (Paracem DC). All ceramic samples were treated as recommended by manufacturer before the resin application. A loading device was specially designed to apply a steady pressure on the cement layer during its setting for standardization. Spectrophotometric shade analysis were recorded for all the ceramic samples before the application of resin, and afterthe application of the resin at the following intervals: After 1 hour, 1 week, 1 month, 3 months, and 6 months. Data was collected to detect effect of polymerization mode of resin cement on final color of the two machinable ceramics used. Results: According to the effect of ceramic material; IPS e.max CAD showed statistically significantly higher mean ΔE (1.72) than IPSEmpress CAD (1.66), regardless the effect of resin luting material or time intervals tested.Regarding the effect of luting material on total color change, regardless the effect of the ceramic material type and time intervals, the Paracem resin cement showed the statistically significantly highest mean ΔE (1.88), this was followed by RelyX Unicem (1.70), where Filtek Z350 (1.51) showed the statistically significantly lowest mean ΔE. According to the effect of time, regardless the effect of ceramic material or resin luting material, there was a statistically significant increase in mean ΔE by time. The statistically significantly highest mean ΔE was found after 6 months(3.23).This was followed by 3 months (2.68), 1 month (1.61) and 1 week (0.59). The statistically significantly lowest mean ΔE was found after 1 hour (0.36). Conclusion: Ceramic, cement, time and the interaction of the three variables had a statistically significant effect on mean ΔE. The IPS e.max CAD ceramic material shows more color change with time than the IPS Empress CAD ceramic material. Dual-cured resin cements (Paracem & RelyX Unicem) show a higher color change than light-cured resin cement (Filtek Z350). Time had an effect on color stability; the more the time the more the color change occurs.