The aim of this study was to investigate, using three-dimensional finite element analysis [3D-FEA], the stress and/or strain distribution of five different resin composites used in combination with carbon fibre posts. FEA models of five different light-cured composites were employed. The stress distribution of composite in combination with carbon fibre post was analysed under two different loading conditions: (i) polymerization shrinkage and (ii) load of 150N with a 35 degrees tilt to the long axis of the tooth. The Material Fatigue Rate [MFR%] of composite materials, dentin and fibre post was calculated. The highest stress values were recorded for Heliomolar and Clearfil-Photo P. The lowest stresses and MFR% values were attained when using Diamond Crown. High MFR% value [>45%] for carbon posts were found in all the tested cases under load. Composite materials with a Young's modulus similar to that of dentin should be selected for the restoration of endodontically-treated teeth when using carbon fibre posts. The peak of the polymerization stress of the composite core is localized at the ferrule level. This might induce an open margin with higher risk of coronal leakage.