Abstract: Nanometer silica particles were added to epoxy resin by the sol-gel method. The mechanical properties such as impact strength, tensile strength and elongation at the break point of the materials were studied at room and cryogenic temperatures. The fracture surfaces were examined by scanning electron microscopy (SEM). The ashes of the composites were collected after burning off the nanocomposites and the silica nano-particles were observed by transmission electron microscope (TEM). At room temperature, the tensile strength and elongation at break attain a peak at approximately 2% silica content where the impact strength reaches the maxium. However, at cryogenic temperature, the tensile strength increases with the increasing silica content. DMA analysis reveals that the glass transition temperature and storage modulus are increased.