Room temperature vulcanized (RTV) silicone rubber-g-polyhedral oligomeric silsesquioxanes (POSS) was prepared and its thermal degradation behavior and thermo-oxidative stability were investigated by thermogravimetric analysis (TGA). The results demonstrated that the chemical incorporation of POSS into polydimethylsiloxane (PDMS) chains significantly enhanced thermal stability of RTV silicon rubber in both nitrogen and air atmosphere. The degradation behavior was further monitored by TGA coupled with real time Fourier transform infrared spectra (FTIR), and the residues were characterized by FTIR and X-ray photoelectron spectroscopy (XPS). It was found that the remarkable improvement in thermal stability could be attributed to the following reasons: (1) the branched structure of RTV silicone rubber-g-POSS and interaction between POSS molecules and PDMS chains; (2) POSS traps generated and grafted or cross-linked structure formed; (3) intumescent ceramic protective barrier formed; (4) the perfect distribution of POSS in RTV silicone rubber-g-POSS. Display omitted