Statement of problem: Assessment of lithium silicate ceramics as regard to its thickness variances  need evaluation with regard to color match to shade guide.   Purpose: This study aimed to investigate the effect of ceramic thickness and foundation restoration  on color production of lithium silicate glass- ceramics.   Material and Methods: A total of 60 rectangular plate slices disks of shade A1 were prepared from CAD/ CAM generated all-ceramic materials IPS e.max CAD (EM) and Vita suprinity blocks(ZLS),   with different thickness (1mm, 1.5 mm and 2mm). The color of ceramic specimens before and after bonding to foundation blocks were measured using a reflectance spectrophotometer and CIE L*a*b* (Commission Internationale de L'Eclairage) color system were used for calculation of color parameter.  The collected data were statistically analyzed using two-way ANOVA and the Tukey HSD test (α=.05).   results: The 2-way ANOVA showed that the ceramic material composition (P<.05), ceramic thickness (P<.05) and tooth foundation all significantly affected ΔE values (P<.05).   conclusions: Reinforcement of CAD/CAM lithia silicate glass-ceramics by zirconia decreases the color match. Acceptance level between the two tested ceramic materials and thickness varied. At all evaluated thicknesses before bonding to foundation blocks, EM presented higher shade matching compared to ZLS. The effect of non tooth colored foundation can be overcome by increasing the thickness of fabricated restoration to enhance color production.