The hybrids of graphene oxide (GO) encapsulated nano-SiO2 (SiO2-GO) were introduced into phenolic resin (PR) to enhance thermal stability of PR. The effect mechanism was investigated in detail. Through electrostatic self-assembly method, the SiO2 nanoparticles were evenly distributed onto the surface of GO. This structure could not only prevent the aggregation of nano-SiO2, but also alleviate the phenomenons of crimp and stack for GO sheets in PR. Nano-SiO2 and GO showed elaborate synergistic effect on thermal stability of PR. Compared with the pristine PR, the 2 wt% SiO2-GO/PR composite showed higher T-5%, T-10%, and T-dmax, which were increased by 65.39, 62.23, and 23.17 degrees C, respectively. And the char yield at 800 degrees C increased from 64.78% to 69.38%. Thus, SiO2-GO hybrids can facilitate the application of PR in the fields of heat insulation and ablation resistance. POLYM. ENG. SCI., 58:2143-2148, 2018. (c) 2018 Society of Plastics Engineers