Abstract: Carbon fibers (CFs) were surface oxidized and aminated，respectively. The influence on the element contents and functional groups of the fiber surface was investigated with X-ray photoelectron spectroscopy (XPS). The oxygen content increased significantly and the (O+N)/C ratio was comparably higher after oxidation treatment. The oxygen content decreased while the nitrogen content increased as formation of amino groups after amination treatment. The soakage of water and epoxy resin to CF surface was characterized by the contact angle which was measured through the insert method and liquid droplet method，respectively. As a result，the contact angle of CFs with respect to epoxy resin was found to be remarkably decreased. The contact angle of the aminated CFs with respect to epoxy resin was lower than that of the oxidized ones，which proved surface amino group increment to be a stimulative factor on the soakage of epoxy resin to CFs.