Objective To evaluate the use of dental operating microscope in treating calcified canals. Methods 369 calcified canals were treated with C⁃Pilot files and ethylene diamine tetraacetic acid (EDTA) under dental operating microscope. The canals were grouped based on the calcified teeth site and calcified location in canals, and then the suc⁃ cess rates of negotiating were analyzed with c2 test. Results 310 of 369 calcified canals were negotiated under dental operating microscope, the negotiating rate was 84.01%. For the anterior, premolar and molar, the negotiating rate were 94.78%, 85.98%, and 74.15% respectively. There were significant differences between anterior and molar teeth (c2 = 19.658, P＜0.05). When the calcification was located in straight canals or above the root canal curvature, canals were negotiated with a success rate of 96.85%. However, it decreased to 39.76% when the calcified portion located below the root canal curvature (c2 = 156.113, P＜0.05). Conclusion It is an effective way to use dental operating microscope and C⁃Pilot files to treat calcified canals, but the therapeutic effects might be affected by sites of the teeth and the calci⁃ fied location in canals.