Objectives: This study aimed to determine the effect of changing the field of view on the ac- curacy of Cone Beam Computed Tomographic assessment of alveolar bone loss in periodontal defects.   Materials and methods: 73 natural human teeth naturally attached to ten dry human jaws were used with small linear gutta percha pieces with central indentation glued on their facial and lingual/ palatal surfaces at the place of CEJ, to be used as marker for alveolar bone level measurements both directly using digital caliber with an accuracy of 0.01 mm and radiographically on three CBCT images for each tooth obtained at three different field of views (FOV) (80×80 mm, 100×100 mm and 200× 100 mm) using a standardized voxel size of 0.2 mm, the direct and CBCT measurements were then compared. Results: there was no statistically significant difference between the mean CBCT measure- ments errors at different FOVs. The average CBCT measurements error in the three FOVs (80 × 80mm, 100 × 100 mm and 200× 100 mm) were 0.23±0.09 mm, 0.24± 0.10 mm and 0.21 ± 0.09mm respectively. Conclusions: The FOV size has no significant effect on the CBCT measurements accuracy of the alveolar bone level.