The current article describes a novel approach to produce the carbon fiber/phenolic matrix composites. The composites are focused on the carbon fibers and interfacial behavior. The washed, oxidized, and flexible towpreg-treated carbon fiber is investigated by tensile strength. To relate the interfacial behavior with the characteristics of the components, the surface free energy of the carbon fibers is carried out by capillarity. Thereafter, the tensile strength of carbon fiber strands, the interlaminar shear strength, and the flexure strength are measured. The results show that appropriate treatments could effectively improve the mechanical properties. Interfacial adhesion between the carbon fibers with phenolic resins being fractured under deformation and the dispersed resins on the flexible towpreg carbon fiber are, respectively, studied by scanning electron microscopy and optical microscope. (c) 2008 Wiley Periodicals, Inc.