Purpose: this study aimed to determine the effect of changing the voxel size and the field of view FOV on the accuracy of Cone Beam Computed Tomographic CBCT assessment of alveolar bone loss in periodontal defects.Methodology: The study conducted on 73 natural human teeth (30 molars, 19 premolars and 24 anterior teeth) found in five maxillae and five mandibles. Each skull and its corresponding mandible were scanned with five different CBCT protocols which were organized to provide three scans made at the same FOV (80 × 80 mm) with three different voxel sizes (150, 200 and 400 μm), and three scans made with the same voxel size (200 μ) at three different FOVs (80 × 80, 100 × 100 and 200× 100 mm). On each scan, CBCT measurements of alveolar bone loss were made on each tooth at six sites. Then real measurements were taken directly on the jaws at the same six sites using digital caliber.Results: There was a statistically significant difference between the CBCT measurement errors at different voxel sizes with the 400 μm voxel size showed the highest error. No statistically significant difference was found between the mean CBCT measurements errors at different FOVs. While a statistically significant difference between them was found between different teeth types with the lowest average measurements error was in the premolars.Conclusions: Changing the voxel size significantly affects the CBCT measurements accuracy of the alveolar bone height in periodontal defects, while the FOV size has no significant effect on this accuracy. The least mean CBCT measurements error of alveolar bone loss in periodontal defects is in the premolars region.