In this article, a novel latent curing agent, octa(paratoluenesulfonic acid ammomium salt) (OPAAS) polyhedral oligomeric silsequioxane was synthesized and used in modifying the polybenzoxazine/2,2'-(1,3-phenylene)-bis(4,5-dihydro-oxazoles) (PBO) (PBZ/PBO) resin. The liberated octa(aminophenyl) silsesquioxane and paratoluenesulfonic acid can catalyze the ring-opening reaction of benzoxazine (BZ) resin. The initial curing temperature (Ti), peak curing temperature (Tp) and the Enthalpy of the curing temperature had significantly decreased with respect to pristine BZ/PBO resin. When the OPAAS amount was 3 wt %, the peak curing temperature decreased from 233.7 to 218.2 degrees C. Also, PBZ/PBO/OPAAS composites exhibited better storage modulus than pure PBZ/PBO resin. Meanwhile, PBZ/PBO/OPAAS composites are more thermally stable than PBZ/PBO resin. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012