Background/Purpose: The purpose of this in vitro study was to evaluate the effect of two milling techniques (CAD/CAM and MAD/MAM), two finish lines (Shoulder of 1mm and deep chamfer of 0.8mm) and cementation on marginal accuracy of zirconia endocrown. Materials and methods: Twenty intact maxillary premolars were selected, without any carious lesion or apparent fracture, with similarity in size and shape. Teeth were cleaned then stored until required for experimentation. All specimens were endodontically treated crown portion of all teeth was sectioned perpendicular to long axis of tooth above the cementoenamel junction (CEJ). Teeth were divided into two groups: one prepared with shoulder finish line of 1mm and the other with deep chamfer finish line of 0.8 m. Teeth were prepared with 2mm ferrule with occlusal taper of 10ᵒand 10ᵒ divergence of pulp chamber. All specimens were restored with CEREC 3D CAD/CAM and MAD/MAM (Zirkonzahn) systems using a full anatomical translecent zirconia. All specimens were cemented with rely x unicem and became ready for testing. The vertical marginal gap was measured using the high resolution digital microscope with a fixed magnification of40x. Results: Regarding the processing techniques, it was found that CAD/CAM recorded statistically non-significant (P>0.05) lower vertical marginal gap mean values than copy milling. Regarding the margin design, it was found than chamfer margin design recorded statistically (P<0.05) higher vertical marginal gap values than shoulder one. Influence of cementation: totally marginal gap mean values after cementation was statistically significant (P<0.05) higher than before cementation. Conclusion: The Cerec system recorded lower vertical marginal gap mean values than copy milling .Chamfer margin design recorded significant higher vertical marginal gap mean values than shoulder one. Finally, totally marginal gap mean values after cementation was higher than before cementation.