Poly(aryl acetylene) (PAA) modified by vinyl trimethoxysilane (VTMS) was successfully prepared from a blend of diethynyl benzene (DEB) and VTMS. Scanning electron microscopy and Fourier transform infrared spectroscopy investigations showed that VTMS was copolymerized with DEB. Thermogravimetric analysis revealed that PAA modified by VTMS had a better thermooxidation stability than PAA. Through the application of postirradiation and posthydrolysis, the thermal stability in nitrogen and in air of PAA modified by VTMS was greatly improved. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40158.