The aim of this study was to compare the mechanical properties of a prefabricated root canal post made of carbon fiber reinforced composites (CFRC) with metal posts and to assess the cytotoxic effects elicited. Flexural modulus and ultimate flexural strength was determined by 3 point loading after CRFC posts had been stored either dry or in water. The bending test was carried out with and without preceding thermocycling of the CFRC posts. The cytotoxicity was evaluated by an agar overlay method after dry and wet storage. The values of flexural modulus and ultimate flexural strength were for dry stored CFRC post 82 +/- 6 GPa and 1154 +/- 65 MPa respectively. The flexural values decreased significantly after water storage and after thermocycling. No cytotoxic effects were observed adjacent to any CFRC post. Although fiber reinforced composites may have the potential to replace metals in many clinical situations, additional research is needed to ensure a satisfying life-span.