Abstract: The surface of polyacrylonitrile (PAN)-based carbon fibers (CFs) was modified by anodic oxidation and characterized by atomic force microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and dynamic mechanical thermal analysis. It was found that the roughness and specific surface area of the carbon fibers were increased after oxidation treatment. The contents of hydroxyl and carbonyl groups of the treated PAN-CFs were higher than those of the untreated ones. The loss tangent peak value (tanδmax) of the treated carbon fiber reinforced epoxy resin composites (CFRP) declined compared with the untreated ones, and the glass transition temperature of the epoxy resin was increased. The interlaminar shear strength (ILSS) of the CFRP can be increased by 25% under an appropriate oxidative treatment, and the loss of tensile strength was only 5%. The interfacial adhesion parameters A and α were quantitatively evaluated, and their values were consistent with the results of ILSS of CFRP.