Free radical polymerization of vinylic monomers in the presence of carbon fibers results in the grafting of polymers onto the carbon fiber surface. Graft polymers cannot be removed by intense washing with good polymer solvents. The density and size of these structures are successfully controlled by reaction conditions. Grafting of the carbon fiber surface with hydroxyethyl methacrylate allows for introducing functional groups suitable for the reaction with an epoxy-based resin. The resulting fiber-reinforced composites show enhanced mechanical properties compared to samples prepared from carbon fibers equipped with a standard sizing for epoxy resins. Thus, tensile strength increases by 10%, while interlaminar shear strength improves by 20%.