Among the referral reasons of endodontic problems from general dental clinics to the root canal specialties, 'calcified canal' is the number one. Secondly in order is that 'the symptom does not disappear' and 'root canal retreatment'. This case is a 27-year-old woman with calcified root canal of tooth 47 (FDI) underwent root canal treatment at the local dental clinic for several times and transferred to our endodontic department of hospital for further evaluation and treatment. The patient has no known drug or food allergy, and there are no other systemic diseases. After X-ray and clinical examination, the clinical diagnosis was defined as incomplete root canal treatment with chronic apical periodontitis of tooth 47. The same diagnoses were made on its neighbor tooth of 46 and tooth of 36, which needed to be received root canal retreatment. Non-surgical root canal treatment was adopted after communication combined with operative microscope observation. All of teeth were preserved after the above treatment and the symptom is totally dispelled.