The influence of oxygen plasma treatment on surface properties of poly(p-phenylene benzobisoxazole) (PBO) fibers and aging effect of the oxygen plasmamodified PBO fiber surfaces were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and dynamic contact angle analysis (DCAA), respectively. The results indicated that the oxygen plasma treatment introduced some polar groups to PBO fiber surfaces, enhanced surface roughness and changed surface morphologies of PBO fibers by plasma etching and oxidative reactions. Surface wettability of PBO fibers may be significantly improved by increasing surface free energy of the fibers via oxygen plasma treatment. Aging effect of the oxygen plasma treated PBO fibers showed that the fiber surface wettability degraded in the first several days after the plasma treatment, and it was found to be changeless as the aging time continued as long as 30 days. (c) 2008 Elsevier B.V. All rights reserved.