A high temperature vulcanized (HTV) silicone rubber/octavinyl polyhedral oligomeric silsesquioxane (POSS) hybrid was prepared. The micromorphology of the cured hybrid was investigated by scanning electron microscopy (SEM); the thermal degradation stability of this hybrid was studied by means of thermal gravimetric analyses (TGA); the degradation kinetics of this hybrid was also studied using Doyle method and Coats-Redfern method. Results showed that aggregation of self-cross-linked octavinyl POSS appeared in the HTV silicon rubber/POSS hybrid. The incorporation of POSS into silicon rubber networks enhanced the thermal degradation resistance of the matrix. Activation energy derived by the Coats-Redfern method (142.24 kJ/mol) showed a good agreement with the mean value derived by the Doyle method (146.51 kJ/mol); the thermal degradation reaction of the hybrid followed a three-dimensional diffusion law (D4).