Objective: To in-vitro evaluate the influence of two different matrix systems and curing light intensities on the proximal contact tightness (PCT) of MO cavities restored with two different resin composite restorations. Methods: 96 Ivorine lower left first molar teeth with standardized MO cavities were randomly divided into two main groups according to type of resin composite, the first group was restored using low-shrinkage Filtek LS (3M/ESPE) and the second was restored using Filtek Supreme Plus (3M/ESPE). Half of each group was restored using sectional matrix (Garrison Ring, Composi-Tight® Soft-FaceM 3D-Ring, Garrison dental) and suitable size of wedge; and the other half was restored using circumferential contoured matrix and Tofflemire matrix retainer (Dixieland contour matrix band .0015, Waterpik, Teledyne Getz). Half of each group was light cured using low intensity light (LI 550 mW/cm3) IQ2 Dentsply and the other half was cured using high intensity light (HI 1100 mW/cm3), Dem light, Kerr (n=12). All prepared teeth were mounted in a manikin head to simulate clinical environment. PCT was measured using the Tooth Pressure Meter (University of Technology, Delft). Data were analyzed using one-way ANOVA and Tukey post-hoc (p<0.05). Results: Statistical analysis revealed significant difference between all tested groups (at 0.05 level) except between group 3 & 5 and between group 6 & 7. The use of the low-shrinkage composite resulted in statistically significant tighter proximal contacts compared to nanohybrid composite when polymerized using the same curing light intensity and the same matrix system (p<0.001). For the same composite material, the low-intensity curing light resulted in statistically significant tighter proximal contacts than the high-intensity curing light. Also, the use of sectional matrix system and separation ring resulted in significantly tighter proximal contacts than circumferential matrix and retainer except for group 6 and 7, which revealed no significant difference. Conclusions: Sectional matrix with a separation ring creates a proper proximal contact tightness of class II posterior composite restorations. Light curing unit intensity as well as type of composite material may influence the proper proximal contact tightness of class II posterior composite restorations.