Objective To investigate the root canal curvature in Chinese mandibular permanent incisors. Methods Two hundred and ninety nine Chinese mandibular permanent incisors were included in this study. The root canals were inserted with stainless steel 15# K files, and then taken radiography from the facial and proximal view by X-ray paralleling technique. Canal curvatures were evaluated by measuring the angle, the radius of the curvatures, and the length of the curved part of the canal. Based on the curved angle and the shape of curved canals, the root canals were classified. Results The curved angle, radius, and the curved canal length was 5.28°±5.52°, 16.19 mm± 12.38 mm, 4.10 mm±2.01 mm, respectively in the facial view; 9.99°±5.84°, 18.86 mm ±9.71 mm, 3.27 mm±2.39 mm, respectively in the proximal view. The prevalence of straight, light, moderate, and serve curved root canals in mandibular permanent incisors was 15.7%, 66.9%, 16.7%, and 0.7%, respectively（P
