High strength carbon fibers were electrochemically treated in an aqueous ammonium carbonate solution, with increasing electric current density, using an original continuous treatment process. The electrochemical treatment induced a modification of the surface properties, i.e., surface functional groups as observed by XPS. As a result, the O-1s/C-1s and the N-1s/C-1s ratios of the fiber surfaces increased with the increase of current intensity of the electrochemical treatment in the interval of about 30-50 A m(-2). However, no significant change in the surface functional activity characters was observed for strong treatments. Hence, a moderate treatment (30 A m(-2)) was sufficient to obtain optimum (O-1s + N-1s)/C-1s ratios in this system. This treatment is possibly suitable for carbon fibers to be incorporated in a polar organic matrix, resulting in increasing the interlaminar shear strength (ILSS) of the resulting composites.