A UV testing chamber was designed and prepared for testing the UV-resistance of poly(p-phenylene benzobisoxazole) (PBO) fibers. The optimum conditions for the test were established by measuring UV irradiation at a chamber position using various kinds of UV sources and different irradiation times. Expectedly, PBO fibers (Zylon$^{(R)}$) showed significant degradation under UV irradiation by exhibiting a decrease in the tensile strength and elongation of up to 37% and 18%, respectively. Selected UV-absorbing and -stabilizing agents were successfully coated onto the fibers using water-borne polyurethane. It was found that triazine-type UV absorbing agents were more effective than benzophenone- or benzotriazole-type agents in reducing the degradation of PBO fibers under UV irradiation.