A surface modification method of PBO fiber----fibrillation combined with oxygen plasma treatment was employed in this paper. The surface chemical structure and morphology of PBO fiber were characterized by the methods of FTIR, XPS and SEM. The corresponding change in the surface contact angle was evaluated by the dynamic contact angle system. The degree of the fibrillation was measured by the BET test and the specific area of the fiber was increased sharply as well. Otherwise, the polarity and wettability of the fiber were greatly improved by the oxygen plasma treatment. From the results, it can be suggested that the fibrillation combined with oxygen plasma treatment is an effective surface modification method for PBO fibers, and the fibers which were treated by this method can be used as the reinforcement fibers in friction and sealing materials or used to manufacture the specialty paper.