The purpose of this study was to investigate radiographic features of the C-shaped canal system in mandibular second molars and their relationship to the canal anatomy by using intraradicular contrast medium and micro-computed tomography (microCT) scanning. Thirty mandibular second molars with fused roots were collected and stored in 10% formalin solution. After being scanned by microCT and reconstructed with 3-dimensional software, the pulp tissue of each tooth was removed mechanically and chemically. The contrast medium was introduced into the canal by using a specialized device, and the buccal-lingual radiograph was taken for each tooth. The radiographic images were classified into 3 types: Types I (merging type), II (symmetrical type), and III (asymmetrical type). The relationship between the radiographic and anatomic features was analyzed by collating the microCT scanned canal images with the radiographic types. The results were subject to Kruskal-Wallis test. Findings showed that 10 teeth were Type I, 10 teeth Type II, and 10 teeth Type III. Types I and III had more C1, C2 canal shape in their canal orifice, coronal, and middle canal portion than the Type II (P < .05). Types II and III had more C3a, C3b canal shapes in the apical canal portion than Type I (P < .05). On the basis of these results, the radiographic features revealed by the intraradicular contrast medium can help to identify the canal anatomy of C-shaped canal system in mandibular second molars.