In this work, O-3 modification method was used for the surface treatment of polyacrylonitrile (PAN)-based carbon fiber. The surface characteristics of carbon fibers were characterized by X-ray photoelectron spectroscopy (XPS). The interfacial properties of carbon fiber-reinforced polyamide 6 (CF/ PA6) composites were investigated by means of the single fiber pull-out tests. As a result, it was found that IFSS values of the composites with O-3 treated carbon fiber are increased by 60% compared to that without treatment. XPS results show that O-3 treatment increases the amount of carboxyl groups on carbon fiber surface, thus the interfacial adhesion between carbon fiber and PA6 matrix is effectively promoted. (C) 2008 Elsevier B. V. All rights reserved.