Objective: This prospective study aimed to evaluate the clinical performance of different restorative materials in primary molars with class II carious lesions. Materials and Methods: A total of 160 class II carious lesions (with radiographic involvement of the outer half of dentin) in 30 patients were randomly divided into four groups and restored with a glass ionomer restorative system (Equia™), two different bulk-fill composites (Sonicfill™ and X-tra fil™), and a nanohybrid composite (Filtek Z550™). The restorations were clinically and radiographically evaluated at the baseline, and 3, 6, and 12 months according to the modified United States Public Health Service criteria. Statistical analyses were performed using Pearson's Chi-square and McNemar tests. Results: After 1 year, 134 restorations were evaluated in 26 patients. Equia was statistically less successful than the other restorative materials in marginal adaptation and retention criteria (P < 0.05). However, no material was found to be superior to the others over the study period in marginal discoloration, color matching, secondary caries, anatomical form, and postoperative sensitivity (P > 0.05). Conclusion: The bulk-fill and conventional composites exhibited good clinical performance, and Equia exhibited minor changes over the 1-year trial period.