Benzoxazine bearing trimethoxylsilane (BA-b) was successfully synthesized via Mannich condensation among phenol, paraformaldehyde, and gamma-aminopropyltrimethoxysilane. The hydrolysis and condensation of the BA-b catalyzed by hydrochloric acid can afford a soluble polysilsesquioxane bearing benzoxazine groups (denoted PSSQ-b). By initiating the cocuring reaction of PSSQ-b with difunctional benzoxazine of bisphenol A (BA-a), the inorganic-organic hybrids of polyberizoxazine with polysilsesquioxane were prepared. The hybrids displayed enhanced T-g's in comparison with the control polybenzoxazine. In terms of initial decomposition temperature (T-d) and char and ceramic yields, the hybrids exhibited improved thermal stability as shown by thermogravimetric analysis (TGA). (c) 2005 Wiley Periodicals, Inc.