Background and Objectives: Internal Root Resorption (IRR) occurs in pulpchamber and canals of the toothand results in desolation of around dentin. Regarding to important role of early diagnosis of IRR in prognoseand treatment plan of the teeth and also limitations of intraoral technics in early detecting of theselesions, in this study we evaluated the accuracy of PSP in diagnosis of these lesions. Subjects and Methods: We split 70 single root premolar teeth mesiodistalyand made artificial IRR in 35teeth. The rest of them used as control group PSP and Conventional radiography captured from all teeth. IRR existence or not was considered in PSP and Conventionalradiographies of each tooth. Results: PSP has complete agreement in all cases with reality but Conventional radiography in some casesparticularly in 1/3 apical lesions of the root has moderate accuracy with reality and its results diden’, thave considerable differences with reality. Conclusion: Regarding to this study, has higher accuracy for PSP than Conventional radiography in detectingInternal root resorption lesions particularly in apical sites.