Bisphenol A epoxy rosin was modified by dimethyldichlorosilane(DMS),or the mixture of DMS and α, ω-dichloro-polydimethylsiloxane(DPS)．The connections between the properties of the modified systems and the composition and content of the organic silicons were investigated by measuring the impact strength,tensile strength,elongation, and glass transition termperoture(Tg) of the cured materials．The results showedthat,aftermodification with DMS of 5.7 phr．the materials exhibited improved impact strength (20.2 kJ/m2),tensile strength (67.0 MPa),elongation(11.3％) and Tg(168.0℃),which all were higher than those of the pure epoxy resin,they wero 10.8 kJ/m2, 45.9 MPa,5.9％ and 135.4℃,respectively．For materials modified by the mixture of 0.7 phr DMS and 10 phr DPS．the properties wero further improved especially,the impact strength reached 31.6 kJ/m2 and the elongation reached 81.6％．The fracture surfaces of the modified resins were investigated by scanning electronic microscopy(SEM)．They showed typical characteristics of tough plastics,and for the one modified by 0.7 phr DMS +10 phr DPS many microparticles were observed which were supposed to be related with the significant increase in impact strength．