Polymethyl(3-glycidyloxypropyl)siloxane (PMGS) was synthesized as a flame-retardant additive, which were cocured with diglycidyl ether of bisphenol-A (DGEBA) using 4,4'-diaminodiphenylsulfone as a curing agent. The structure of PMGS was confirmed through Fourier transform infrared and 1H-NMR spectra. The cured products were characterized with dynamic mechanical thermal analysis, thermogravimetric analysis, and oxygen index analyzer. With PMGS incorporated, the cured epoxy resin showed better thermal stability, higher limited oxygen index, and higher char yield. At moderate loading of PMGS, the storage modulus and glass transition temperature of the cured epoxy resin based on neat DGEBA were obviously improved. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011