Objective:To evaluate the prevalence of C-shaped canals and radicular grooves(RG)in mandibular premolars using cone-beam computed tomography(CBCT)and explore the correlation between these features,gender and bilateral sym-metry.Methods:CBCT images of 272 patients with an age group of 60～70 years were selected from pre-existing database.The prevalence of C-shaped canal and RG was recorded along with variables such as age,sex,and bilateral prevalence.Results:The prevalence of C-shaped configurations in the mandibular fist premolars was higher than the mandibular second premolars(12.5％vs.0.93％,P＜0.05).CBCT analysis revealed that in cervical third,84.29％of canals were found to be C4 type.A high prevalence of C2 type canal was found in middle(65.71％)and apical third(34.29％).The prevalence of RG in the man-dibular first premolars was higher than the mandibular second premolars(13.85％vs.3.08％,P＜0.05).Conclusion:This study showed a high prevalence of C-shaped canals and RG in mandibular fist premolars as compared with mandibular second premolars.Except the gender factor,the incidence of C-shaped root canal and RG symmetry is higher.Compared with other re-search methods,in vivo CBCT is more accurate and efficient for assessing the complex structure of the root canal configuration(such as C-type root canal and Radicular groove).