Abstract: Polyhedal oligomeric silsequioxane (POSS)/ethylene-propylene-diene-monomer rubber (EPDM) hybrid materials were prepared by twin roller mixing with octaphenylsilsequioxane (OVP), EPDM and vulcanizing agent.The mechanical properties and the flame retardcy of the hybrid materials were studied.The thermal stability and heat release rate (HRR) of the hybrid materials were investigated with thermo gravimetric analyzer and cone calorimeter.Comparing with the pure EPDM, the limited oxygen index (LOI) and thermal stability of POSS/EPDM with OVP are increased dramatically, the p-HRR of POSS/EPDM with OVP is decreased remarkably.The LOI is increased by 11.8%, the temperature of degradation is increased by 51℃, the HRR is decreased by 25.8%, the content of residue is 1.58 times as that of pure EPDM when 0.88% mass fraction OVP is added.The results show that OVP has great application value.