Aim: The purpose of this study was to evaluate the diagnostic accuracy of digital Periapical radiography and Cone-beam Computed Tomography in Detection of Simulated External Root Resorption. Subjects and methods: This study was initiated with sample selection calculation 90 maxillary central incisors teeth. Round burs in 3 different size small, medium large were used to create simulated cavity in cervical, middle and apical root third. Digital caliper used to measure the simulated cavity. Teeth were covered by wax and mounted in block made from silicon impression putty and placed in phantom to simulated soft tissue. CBCT scan was made and digital preapical radiograph PSP was taken then the images were analysis and compared with the result gathered from digital caliper. Results: Digital preapical radiograph PSP clearly detected the simulated cavity CBCT showed statistically significantly lower mean cavity measurement than the actual measurement at cervical, middle and apical root levels (P-value <0.001), (P-value <0.001) and (P-value = 0.001), respectively in large cavity . Conclusion: Under the condition of present study, it can be conclude that there was no difference in accuracy of identifying defects between digital periapical radiographs PSP and CBCT images