Poly (p-phenylene benzobisoxazole) (PBO) fibers were functionalized by 3-Glycidoxypropyltrimethoxysilane (KH-560) and then coated with 1 H, 1 H, 2 H, 2H-Perfluorodecyltrimethoxysilane (HFTES) and UV absorber (UV-328) to improve hydrophobicity and UV aging resistance. The chemical compositions of PBO fibers before and after modification were analyzed by XPS and surface morphologies were observed by SEM. The hydrophobicity of PBO fibers was evaluated by the measurement of contact angle for water and the UV aging resistance was evaluated by the tensile strength retention ratio of PBO fibers. The results showed that KH-560 was successfully introduced onto the PBO fiber surface. The contact angle for water was increased by 128% from 51.7° to 127°, suggesting a huge improvement of hydrophobicity. The UV aging resistance of PBO fibers was also greatly improved. After 400 h UV exposure, the tensile strength retention ratio was increased to 53%, which was much higher than that of 21.4% for pristine PBO fibers. And the results of variable coating times demonstrated that the optimal UV aging resistance was obtained by coating three times.