This study was carried out to determine the design and thickness of the cervical margin of a castable ceramic restoration from the point of view of its castability. Castability of castable ceramics was lower compared to Ag-Pd-Au and Co-Cr alloy with the use of the mesh pattern and rod pattern test (p < 0.05). It was more dependent on the pattern thickness than alloys (p < 0.05), and perfect reproducibility with non-measurable variability could be estimated to reach 1.0 mm thickness of the original pattern (p < 0.001). Marginal shape was certainly more reproducible in a right angle shoulder than in 30, or 45 degree bevels (p < 0.05). From these results, it is suggested that a right angle shoulder margin with 1.0 mm thickness is more suitable to castable glass ceramic restoration than any other design.