Aim: The aim of this randomized, controlled, single centre clinical trial was to evaluate the one year clinical performance of CAD/CAM fabricated resin nano-ceramic inlay restorations in two surface class II cavities in comparison with direct posterior composite restorations. Materials and Methods: One hundred and twenty 2-surface (MO/OD) carious lesions or old restorations that needed to be replaced were included and randomly assigned into two groups. The restorations in experimental group were fabricated by a CAD/CAM system with resin nano ceramic blocks (Lava Ultimate, 3M ESPE, USA), while a posterior nanohybrid composite resin (Clearfil Majesty Posterior, Kuraray, Japan) was used for direct posterior composite restorations in control group with a three-step etch & rinse dentin adhesive system (Optibond FL, Kerr, USA). All tested restorative materials were used according to the manufacturers' instructions. Clinical evaluation was performed after 1 week, 6 months and 1 year according to the FDI criteria. The data were analysed using Friedman's ANOVA and Mann-Whitney U tests ( = 0.05). Results: After 1 year, all restorations were clinically acceptable with no need for clinical attempt. Considering all criteria, the differences between two groups were not statistically significant. Only surface lustre of direct composite restorations significantly reduced to score 2 after 1 year (p =0.046). Conclusion: The clinical performance of CAD/CAM fabricated resin nano ceramic inlay restorations was found successful according to FDI criteria after 1 year.