A novel polyhedral oligomeric octamethyldiphenylsulfonylsilsesquioxane (OMDPSS) was synthesized from octaphenylsilsesquioxane and benzenesulfonyl chloride via a Friedel-Crafts reaction in high yield. OMDPSS was characterized by Fourier transform infrared spectroscopy, H-1 NMR, C-13 NMR, and Si-29 NMR spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), wide-angle X-ray diffraction, differential scanning calorimetry, and elemental analysis, and found to be an amorphous polyhedral oligomeric silsesquioxane with a (RSiO3/2) 8 structure. OMDPSS exhibited good solubility in commonly used solvents and superior thermal stability according to thermogravimetric analysis. Its initial thermal decomposition temperature (Td5%) was found to be 401 degrees C in air and 428 degrees C in nitrogen.