OBJECTIVE To evaluate the role of dental operating microscope in clinical treatment of lower incisors with multiple root canals. METHODS 143 mandibular incisors in 128 patients were treated endodontically. Two kinds of preoperative radiographs were taken for each tooth, using straight projection and eccentric projection. The root canal morphology was recorded according to Vertucci's classification. Under dental operating microscope, the teeth with multiple root canals were shaped using Ni-Ti rotary instruments Hero 642, cleaned using sodium hypochlorite, and obturated with vertical condensation technique. The following information was recorded: The number of teeth that were found to have multiple canals in two kinds of preoperative radiographs, and when using and without using microscope. The efficiency of preparation and obturation was analyzed with radiographs before, during and after operation. RESULTS The mandibular central incisor with one canal was 73.53% and multiple canals was 26.47% in treated teeth. The mandibular lateral incisor with one canal was 70.67% and multiple canals was 29.33% in treated teeth. By eccentric projection radiograph and treatment using microscope, more teeth with multiple canals were found. No complication was found during root canal preparation. 134 teeth were well filled and 9 showed slight over-filling. CONCLUSIONS With dental operating microscope, the mandibular incisors with multiple root canals could be treated well in combination with rotary instrumentation and vertical condensation technique.