Tetrafluoroethylene-propylene elastomer-octavinyl-polyhedral oligomeric silsesquioxane (TFE/P-OVPOSS) composites containing various percentages of OVPOSS are prepared via room temperature milling and heat vulcanization at 170 degrees C. The composites are characterized by FTIR, C-13-NMR, Si-29-NMR, XRD, DSC, SEM, tensile test, DMA, and TGA. The crosslink bond formation between TFE/P and OVPOSS conforms to the structural characterization of the composites. The OVPOSS cages aggregate when the OVPOSS dosage is more than 6 as observed from the XRD curves and SEM images. The swelling test shows that the experimental crosslink density is lower than the calculated crosslink density, indicating that not all reacted vinyl groups are converted into crosslink bonds. Meanwhile, the incorporation of OVPOSS significantly enhances the mechanical property and elevates the glass temperature of the composites. However, the thermal property is only improved slightly. (C) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1281-1288, 2013