The reaction between octaaminophenyl polyhedral oligomeric silsesquioxane (OAPS) and 2,2-(1,3-phenylene)-bis(4,5-dihydro-oxazoles) (PBO) over different temperature ranges was confirmed by FT-IR spectroscopy. The OAPS was used to modify benzoxazine (BZ) in the presence of PBO. The novel polybenzoxazine (PBZ)-PBO/ OAPS hybrid nanocomposite was prepared by solvent methods. Dynamic mechanical analyses indicated that the nanocomposites exhibited much higher T-g values than the pristine PBZ and PBZ-PBO resin, and the storage modulus of the nanocomposites was maintained at higher temperatures, although only a small amount of OAPS was incorporated into the systems. Dynamic thermogravimetric analysis showed that the thermal stability of the hybrid was also improved by the inclusion of OAPS.