Abstract: SiO₂ hollow microspheres modified Si-containing arylacetylene resin (SiO₂/PSAC) casting was prepared to ameliorate the brittleness of cured Si-containing arylacetylene resin and to improve the mechanical properties of the SiO₂/PSAC resin casting and to meet the need of the application in the field of aeronautics and astronautics. The structure and properties of the SiO₂/PSAC resin casting and quartz fiber reinforced SiO₂/PSAC (QF-SiO₂/PSAC) composites were investigated. The microstructure of SiO₂/PSAC resin castings and QF-SiO₂/PSAC composites were observed by SEM, and the toughening mechanism of SiO₂ was analyzed. The heat resistance and thermal stability of SiO₂/PSAC composites were studied by DMA and TGA. The heat resistance of the resin decreased slightly, but the porous structure made the resin excellent in dielectric properties. Meanwhile, when the content of SiO₂ is added to 2wt%, the flexural strength of SiO₂/PSAC resin casting is 22.3 MPa. The temperature of decomposition (T_d5) is 551℃ and the char yield at 1 000℃ is 86.5%; the flexural strength of QF-2SiO₂/PSAC composite is 298.3 MPa, and the modulus reaches 31.0 GPa, which increases by 27.5% and 59.0%, respectively; When the content of SiO₂ is 5wt%, the shear strength of QF-5SiO₂/PSAC composite increases by 16.0%.