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Aramid fibers (AFs) with their high Young's modulus and tenacity are easy to degrade seriously with ultraviolet (UV) radiation that leads to reduction in their performance, causing premature failure and limiting their outdoor end use. Herein, we report a method to synthesize nano-SiO 2 on AFs surfaces in supercritical carbon dioxide (Sc-CO 2 ) to simultaneously improve their UV resistance, thermal stability, and interfacial shear strength (IFSS). The effects of different pressures (10, 12, 14, 16 MPa) on the growth of nanoparticles were investigated. The untreated and modified fibers were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It was found that the nano-SiO 2 -decorated fibers exhibited improvement of thermal stability and mechanical properties, and the IFSS of the nano-SiO 2 modified fibers increases by up to 64% compared with the untreated fibers. After exposure to 216 h of UV radiation, the AFs-UV shows a less decrease in tensile strength, elongation to break and tensile modulus, retaining only 73%, 91%, and 85% of the pristine AFs, respectively, while those of AFs-SiO 2 -14MPa-UV retain 91.5%, 98%, and 95.5%. In short, this study presents a green method for growing nano-SiO 2 on the surface of AFs by Sc-CO 2 to enhance the thermal stability, IFSS, and UV resistance.