An epoxy matrix system modified by digly-cidylether-terminated polydimethylsiloxane (DGETPDMS) and bismaleimide (BMI) was developed. Epoxy systems modified with 4, 8, and 12% (by wt) of DGETPDMS were made using epoxy resin and DGETPDMS, with diaminodiphenylmethane as the curing agent. The DGETPDMS-toughened epoxy systems were further modified with 4, 8, and 12% (by wt) of BMI, namely (N,N'-bismaleimido-4,4'-diphenylmethane). DGETPDMS/BMI/epoxy matrices were characterized using differential scanning calorimetry, thermogravimetric analysis, and heat deflection temperature analysis. The matrices, in the form of castings, were characterized for their mechanical properties, viz. tensile strength, flexural strength, and impact test, as per ASTM methods. Mechanical studies indicate that the introduction of DGETPDMS into epoxy resin improves the impact strength, with reduction in tensile strength, flexural strength, and glass transition temperature, whereas the incorporation of BMI into epoxy resin enhances the mechanical and thermal properties according to its percentage content. However, the introduction of both DGETPDMS and BMI enhances the values of thermomechanical properties according to their percentage content. (c) 2006 Wiley Periodicals, Inc.