Objectives: this study investigated the effect of the preparation parameters and the cement space width on the internal and marginal fit of a machinable all ceramic crowns. Methods:. A total of forty non anatomical copings were fabricated using the machinable Cerec (In Lab) technique from machinable IPS –Emax CAD blocks. The samples were divided into two groups of twenty copings according to the occlusocervical preparation heights (H) into Group Ι : (H1) = 6 mm occluso-cervical height and Group ΙΙ : (H2) = 4mm occluso-cervical height , then each group was subdivided into two subgroups of ten copings each according to the tested convergence angle (T) into subgroup A : (T1) =120 total convergence angle and subgroup B : (T2) =20º total convergence angle finally each subgroup was further subdivided into two divisions of five copings each according to the tested cement space widths (C) into division i : (C1) =80 μm and division ii : (C2) = 120 μm. The internal fit was evaluated using the cement space replica technique and image analysis , where the silicone block material obtained from each coping were sectioned . The sections were examined at X12.5 magnification as the internal fit for each coping was evaluated by measuring the mean internal gap of four fixed points on one side of each quarter. These points were distributed at the following manner: A.mid occlusally, B. axial one third occlusally, C. axial one third cervically, D.marginal area. The marginal fit was evaluated by the measurement of the vertical marginal discrepancy by the aid of the stereomicroscope as each coping was marked at four quarters by four vertical lines on the die margin and the cervical margin of samples, within each quarter five measurements were taken thus a total of twenty measurements per coping were recorded. Results: The highest mean internal gap values were recorded by (4 mm x 12° x 80 μm) which recorded (0.14±0.05mm), (6 mm x 20° x 80 μm) which recorded (0.14±0.04mm)and (6 mm x 12° x 80 μm) interactions which recorded (0.14±0.03mm) with no statistically significant difference between them at P < 0.05. And 6 mm preparation height with 12° convergence angle and 80 μm cement space width showed the statistically significant highest mean marginal gap (0.31±0.03mm). Conclusion: The internal and marginal fit results of the present study were within the clinically acceptable range. Regarding the internal and marginal fit, at 4 mm occluso-cervical height and the 20º convergence angle concealed the effect of the tested cement spaces. At 4 mm occluso-cervical height and 12º convergence angle, increasing the cement space improved the internal and the marginal fit .Increasing the convergence angle at 6 mm preparation height did not conceal the effect of the tested cement space. In concern of 6 mm preparation height at each convergence angle, increasing the cement space from 80 μm to 120 μm improved the internal and marginal fit.