Siloxane prepolymer were synthesized by epoxy terminated siloxane oligomer onto diamino diphenylmethane(DDM) and bisphenol A(BPA) of melting state. The cured specimen of based siloxane prepolymer were prepared by nixing diglycidyl ether bisphenol A(DGEBA) with 5∼20phr of siloxane prepolymer at reaction temp. 150℃. In DGEBA/polysiloxane system, cured specimen are investigated on mechanical and thermal properties. As a result on mechanical properties, flexural and impact strength were increased that siloxane prepolymer blend ratio increased, on the other hand Tg, thermal expansion coeffi.( α ) and modulus were decreased. The morphology of DGEBA/DDM were showed directly cross-section of fraxture energy flow and DGEBA/SiO system were investigated heterogeneously domain forms,