High-performance fiber poly(p-phenylene benzobisoxazole) (PBO) shows poor anti-ultraviolet (UV) aging properties, which can lead to a significant drop of properties after light irradiation. In order to improve their photo stability, PBO fibers were easily coated with polydopamine (PDA), the mechanical properties, thermal stability and crystal orientation of the initial fibers and dopamine-modified fibers before and after UV irradiation were studied. It is found that the performance of the initial PBO dramatically drops after exposure to UV light, the tensile strength decreases by 67%; the PDA coated PBO fibers show little differences on its mechanical properties, thermal stability and crystal orientation after UV irradiation, the tensile strength only decreases by 33%. The modified PBO fibers can be used to adsorb pollutant such as rhodamine B in water treatment, the adsorption capacity for 24 h reaches up to 0.25 mg/g. A simple and efficient method was successfully developed to enhance the anti-UV properties and functionality of PBO fiber coated with PDA.