Background: The mandibular second molar is the main chewing tooth and often suffer from pulp damage due to the misalignment of the mandibular third molar. In addition, it’s C-shaped root canal system is a challenge for endodontic treatment. This emphasizes the significance of tooth morphology and root canal system study which can contribute to anthropology, as well as Odonto-Stomatology. Purpose: The objective of this study was explore the morphology and root canal system of the mandibular second moalar in order to provide indicators dentistry applications. Materials and methods: Preclinical (in vitro) study was conducted on 48 mandibular socond molars which was collected in Thua Thien Hue province from December 2021 to June 2022. The teeth were measured externally and determine the shape of the roots. The canal system was examined with two methods including clearing technique and Cone Beam CT. Results: The average length of mandibular second molar was 20.37 ± 1.28 mm. 81.2% of teeth had one root, and 18.8% had two. The teeth with C-shaped roots accounted for 31.2%. The majority of distal roots possessed a simple type I (single canal) configuration. While the canal system of mesial roots was more complex which contained two canals, of which type I, II, III, IV were the most prevalent. C-shaped canal morphology was observed in 31.2% of the examined teeth. Conclusion: The root canall system of mandibular second molar was complex, the percentage of C-shaped canal was high (31.2%). There was similarlu results of two methods of clearing technique and Cone Beam CT in examining the root canal system of mandibular second molars. Key words: mandibular second molar, root canal system, C-shaped root, C-shaped root canal.