Abstract Objectives The purpose of this study was to evaluate and compare the clinical performances of two different posterior composites in Class I restorations. Methods In twenty patients a total of 40 Class I cavities were restored with a nanohybrid composite (Tetric EvoCeram) and a low shrinkage composite (Filtek™P90), using their self-etch adhesives. The restorations were clinically evaluated 1 week after placement as baseline, 6, 12 and 18 months post-operatively using modified USPHS criteria by two previously calibrated operators. Statistical analysis were performed using Pearson Qui square and Fisher's Exact Test (P < .05). Replicas were taken to the restored teeth under investigations at each recall period and gold sputtered, to be examined under the SEM. Results Lack of retention was not observed in any of the restorations. With respect to marginal discoloration, marginal adaptation, secondary caries and surface texture, no significant differences were found between two restorative materials tested after 18 months (P > .05). Regarding the surface roughness, no statistical significant difference was recorded, however it was recorded that the results obtained by the tested silorane-based composite were slightly higher. This observation was repeated in describing the % of marginal discoloration of both group I and II at different follow up periods .The difference between both groups was not significance. Restorations did not exhibit post-operative sensitivity at any evaluation period. Concerning the data collected from SEM images no significant difference was recorded comparing both groups at any of the evaluation periods. Conclusions Clinical assessment of Tetric EvoCeram and Silorane composites exhibited acceptable results.