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A series of polyimide/silica (PI/SiO2) hybrid foams were prepared by the sol-gel process. Aminopropyltriethoxysilane was used as the coupling agent to enhance the compatibility between PI matrix and SiO2. Fourier transform infrared spectroscopy and scanning electron microscopy were used to analyze the chemical structure and cellular structure of PI/SiO2 hybrid foams. The results indicated that the three-dimensional network of SiOSi was formed in the hybrid foams, and the hybrid foam presented the uniform cellular structure when the SiO2 content was less than 6 wt%. The thermal stability, dynamic mechanical property, and dielectric property of PI/SiO2 hybrid foams were investigated by dynamic mechanical analysis, thermogravimetric analysis, and vector network analyzer, respectively. The introduction of SiO2 improved the thermal stability and increased the storage modulus and glass-transition temperature. The hybrid foams showed higher dielectric constants compared with the neat PI foam. The erosion resistance to atomic oxygen (AO) of PI/SiO2 hybrid foams was also evaluated in a ground-based AO simulator. The surface morphology and chemical structure of PI/SiO2 hybrid foams before and after AO exposure were investigated by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The results revealed that the inorganic SiO2 protective layers were formed on the surface of PI/SiO2 hybrid foams after AO exposure, which could effectively improve the AO erosion resistance of PI/SiO2 hybrid foams. POLYM. COMPOS., 36:713-721, 2015. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]