Objectives: The aim of the present study was to investigate the root canal configurations of primary mandibular second molars (PMSMs) using Vertucci classification. Materials and Methods: The root canal types of 228 PMSMs (228 mesial and 228 distal roots) were evaluated. In addition, the relationship between external root morphology and Vertucci classification was investigated. The Chi-square test or Fisher Exact Chi-square test was used for the evaluations, and P < 0.05 was considered statistically significant for all tests. Results: The most commonly observed root canal type, which was observed in 228 roots (50%), was Type 4 followed by Type 8 (15.79%), Type 5 (14.47%), Type 1 (9.21%), and Type 3 (6.57%). In 150 mesial roots, the root canal Type 4 was observed whereas the same type was observed in 78 distal roots, and the difference was significant (P < 0.001). In flat roots (82.9%), the most frequently observed root canal type was Type 4 (50.8%) (P < 0.001). Conclusion: Various root canal types were observed in both mesial and distal roots although Type 4 was the most commonly observed. Root canal types showed a consistent relationship with separated and conical root shapes whereas the flat roots showed different root canal types.