objective: This in vitro study evaluated the effect of light curing mode on degree of conversion of resin cement through 3 lithium silicate-ceramics (Lithium disilicate-reinforced glass ceramic (E.max CAD), Zirconia reinforced Lithium Silicate (Celtra Duo) And Zirconia reinforced Lithium Silicate (Vita Suprinity) with different ceramic shades and different ceramic thickness. Materials and methods: 240 samples sliced and separated into 3 groups according to material. Each group subdivided into 2 subgroups according to ceramic shade (A2- B1). Each subgroup subdivided into 2 divisions according to sample thickness (0.5mm -1mm). Each division subdivided into 2 subdivisions according to the light curing mode (Continuous -Pulsating). samples grouped, cemented and scanned using OMNIC 5.1c software connected to the FTIR unit. Results: There was no statistically significant difference in degree of conversion of resin cement between the 3 ceramic types.A higher degree of conversion with B1 shade than the A2 shade. There was a significant effect on degree of conversion with different thicknesses and there was a higher DC% in the continuous light curing than pulsating mode. Conclusions: With respect to ceramic thickness, ceramic type didn't affect degree of conversion of resin cements. Thicknesses up to 1.0 mm and mode of light curing has a significant effect on polymerization of resin cements. Higher degrees of conversion shown with lighter shades.