Display omitted •Chemical modification of epoxy and novolac resins for incorporation into silica/siloxane networks.•Functionalization of CNT with silica nanoparticles to form CNT-SiO2 particle as a nonofiler.•Hybrid nanocomposites prepared by mixing of modified resins with CNT-SiO2 nonofiler and sol-gel method.•Increase of thermal stability and char yield by novolac-based resins and CNT-SiO2.•High char yield of 59.3% obtained from nanocomposites based on modified and epoxidized novolac resins containing CNT-SiO2. Hear, three hybrid composites with high char yield and thermal stability were prepared form tetraethyl orthosilicate (TEOS)-modified epoxy resin (MER), (3-glycidyloxypropyl) trimethoxysilane (GPTES)-modified novolac resin (MNR), epoxidized novolac resin (ENR), and silica-grafted carbon nanotube (SFCNT) by a sol-gel method. The first class was prepared from MER and SFCNT. The second class was prepared from MER, MNR, and SFCNT. And the third class was prepared from MNR, ENR, and SFCNT. TEOS was used as covalent coupling agent in the sol-gel process. Results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed successful modification of epoxy and novolac resins, modification of silica nanoparticles with (3-Aminopropyl)triethoxysilane (APTES), and also functionalization of CNT with amine-modified silica nanoparticles. Results of thermogravimetric analysis confirmed that the hybrid composite containing 4 wt% of SFCNT, MNR, and ENR shows the highest char yield of 58.4%. The hybrid composite containing 4 wt% of SFCNT and MER shows the highest degradation temperature of 442.7 °C. Finally, the hybrid composite formed from 4 wt% of SFCNT, MER, and MNR shows degradation temperature of 439.0 °C and char yield of 47.2%. Microscopic images and X-ray diffraction results confirmed attachment of silica particles at the surface of CNT by chemical bonding.