Epoxy systems containing flexible epoxy and nano-sized particles were prepared and mechanical properties, such as lap-shear and impact-peel strengths were measured. Core-shell rubber (CSR), CaCO3, and SiO2 particles were used as nano sized particles. Polyurethane- and polyamide-modified epoxies were used to form flexible epoxy matrix. As curing agents, DDS (4,4-diaminodiphenyl sulfone) and DICY (dicyandiamide) were used, and 2E4MZ-CNS(1-cyanoethyl-2-4-metylimidazole) was used as catalyst. As an adhesion promoter, zirconate coupling agent was used. CSR has significantly improved impact-peel strengths especially at low temperature, -40 degrees C, due to the presence of highly flexible segments in epoxy backbones. Furthermore, nano-sized inorganic particles, CaCO3, and SiO2, have improved the impact-peel strengths of the epoxy systems. However, the lap-shear strength was decreased as the content of flexible epoxy was increased in epoxy systems.