Purpose: To evaluate and compare the 2-year clinical performance of an ormocer, a nanohybrid, and a nanofill resin composite with that of a microhybrid composite in restorations of small occlusal cavities made in posterior teeth. Materials and Methods: Thirty-five patients, each with 4 occlusal restorations under occlusion, were enrolled in this study. A total of 140 restorations was placed, 25% for each material: an ormocer-based composite, Admira; a nanohybrid resin composite, Tetric EvoCeram; a nanofill resin composite, Filtek Supreme; and a microhybrid resin composite, Tetric Ceram. Two operators placed all restorations according to the manufacturers' instructions. One week after placement, the restorations were finished/polished and patients were advised to return for follow-up at 6 months, 1 year, and 2 years. All patients attended the 2-year visit where the clinical performance of all restorations was evaluated. Two independent examiners made all evaluations according to the USPHS modified Ryge criteria immediately after placement of restorations and at subsequent recall visits. The changes in the USPHS parameters during the 2-year period were analyzed with the Friedman test. Comparison of the baseline scores with those at the recall visits was made using the Wilcoxon signed rank test. The level of significance was set at p 0.05. Results: All materials showed only minor changes, and no differences were detected between their performance at baseline and after 2 years. Only one ormocer and one microhybrid composite restoration had failed after 2 years. No failure was detected in nanohybrid and nanofill composite restorations. Regarding the clinical performance, there were no statistically significant differences among the materials used (p > 0.05). Conclusion: After 2 years, the ormocer, nanohybrid, and nanofill composites showed acceptable clinical performance similar to that of the microhybrid resin composite. Keywords: ormocer, nanofill composite, nanohybrid composite, clinical evaluation