Purpose: To compare the 2-year clinical performance of a silorane-based resin composite with that of an established nanoceramic resin composite for class 1 posterior restorations. Methods: In this randomized controlled study, 100 class 1 molar cavities were prepared in 50 subjects. Each subject received a restoration with Filtek Silorane and Ceram.X Duo in different quadrants. The restorations were evaluated using the modified USPHS criteria at baseline and 6, 12, and 24 months. Parametric changes over the 2-year period were assessed with the Friedman test. The baseline and recall scores were compared by using the Wilcoxon signed-rank test (P< 0.05). Results: No subject developed secondary caries or postoperative sensitivity. Further, the resin composites showed no significant differences in all the evaluated parameters over 2 years (P> 0.05). At 2 years, four Filtek Silorane and seven Ceram.X Duo restorations had Bravo scores for anatomic form, marginal adaptation, and surface texture (P< 0.05); however, these changes were mainly the effect of scoring shifts from Alfa to Bravo. Overall, both materials showed good clinical results with predominantly Alfa scores.