Abstract: A new benzoxazine UV-Bz was synthesized using ultraviolet absorber 4, 4'-dihydroxybenzophenone (DHBP) as material. The corresponding polymer (UV-PBz) obtained by thermal curing of UV-Bz, was a good ultraviolet absorber. Then, UV-PBz was coated on the surface of poly (benzoxazole) (PBO) fiber to study the effect of UV-PBz on the improving photoaging stability of PBO fiber. Fourier Transform Infrared spectra (FT-IR) and ¹H-Nuclear Magnetic Resonance (¹H-NMR) were used to characterize the structure of UV-Bz and UV-PBz. UV-Vis spectra, Scanning Electron Microscope (SEM) and tensile strength test were taken to characterize the photoaging stability of poly (benzoxazole)(PBO) fiber. Results showed that UV-PBz had a wide absorption at the wavelength of about 310 nm. UV-PBz could be coated steadily on the surface of PBO fiber and the photoaging stability of PBO fiber was obviously improved by coating UV-PBz.