External root resorption is one of the rare pathological condition of tooth. It is occurred when periodontal ligament or cementum on the root surface are either damaged or denuded. The causes and classifications have been variously described. Because of the various causes and patterns, and absence of sufficient and consistent evidence for treatment, proper diagnosis and treatment plan based on clinician’s experience and close communication with patient is important. This case report represents the rare case of external root resorption and the treatment. The tooth was retained functionally in oral cavity showing good healing state in 2-year follow-up.