Epoxy blend matrices were prepared by incorporating polyurethane-epoxy into diglycidyl ether of bisphenol-F (DGEBF) type epoxy while SiO2/epoxy nanocomposites were made using DGEBF type epoxy and tetraethylorthosilicate (TEOS) via a sol-gel process. The mechanical properties including tensile and impact properties at 77 K of the matrices and nanocomposites were studied. The mechanical properties at room temperature were also given for the purpose of comparison with the cryogenic mechanical properties. The results showed that the incorporation of polyurethane-epoxy with a proper content into DGEBF type epoxy enhanced the mechanical properties at both room and cryogenic temperatures. Addition of SiO2 nanoparticles to DGEBF type epoxy led to significant increase in tensile strength at cryogenic temperature (77 K) while no evident change in tensile strength at room temperature. In addition, a slight enhancement by the addition of 2 wt % silica while a slight reduction by the addition of 4 wt % silica were observed in impact energy.