This study was designed to assess Effect of finish line and convergence angle on Marginal accuracy of CEREC crowns before and after cementation.Four stainless steel metal dies representing a prepared maindibular first molar design by solid CNC 4 axiss machine.Work software program and synthesized by Feraza.1-The first die was prepared with 12 degree convergence angle and with shoulder finish line 1.2 mm.2-The second die was prepared with 20 degree convergence angle and with shoulder finish line 1.2 mm.3-The third die is prepared with 12 degree convergence angle and with Deep chamfer finish line 0.9 mm.4-The forth die is prepared with 20 degree convergence angle and with Deep chamfer finish line 0.9 mm.The Four stainless steel metal dies was prepared with 5.5 mm occluso-gingival height and 10 mm cervical diameter.A total of 20 ceramic copings (5 for each groups) were constructed on the previously fabricated stainless-steel dies using the CEREC CAD\CAM (computer aided design\ computer aided manufacturing ) The material used in this study was Vita Mark II Blocks. Marginal accuracy was evaluated by seating the copings on their corresponding stainless steel dies and stabilizing on the dies by a specially designed for Marginal fit measurement before cementation and specially designed loading device for Marginal fit measurement after cementation. The measurements were held by the stereomicroscope to assess the the vertical marginal accuracy The stereomicroscope Lecia S8 APO at magnification X20. A total of 20 single measurements were made around each specimen.All data were collected and tabulated , ANOVA was used in testing significance for the effect of finish line type, convergence angle and cementation on mean gap distance. Tukey’s post-hoc test was used for pair-wise comparison between the groups when ANOVA test is significant.