This study evaluated the marginal fit of CAD-CAM Zirconia cores with different proximal height. Thirty Zirconia cores and ten metal ceramics crowns were used to evaluate the marginal gap. The marginal fit was determined to be perpendicular to the tooth axis between the most apical point on the coping margin (core) and the reference marks on the mesial, distal, labial, and palatal surfaces of the die at several key stages of crown fabrication; before porcelain built-up, after body porcelain built-up, and after glazing. Additionally, an opaque stage for the metal ceramic copings was compared as well. Each measurement was carried out with a microscope. The means of gaps among the groups were 58±27 -m, 69±23 -m, 89±29 -m and 80±28 -m, groups I, II, III and IV, respectively. In relation to the proximal and labiopalatal surfaces there were no statistical difference among the groups, except group I. No significant differences were observed in firing stages of all groups. The findings of this study showed that the mean marginal gap of Zirconia cores with different proximal heights fell well within the acceptable clinical ranges.