The introduction of nano-silica particles into an epoxy polymer has increased both the initial toughness, as measured by the fracture toughness, KIc, and also significantly improved the cyclic-fatigue behaviour of the epoxy polymer. Thus, the significant increases recorded in the values of the range of applied stress-intensity factor at threshold, ΔKth, from the cyclic-fatigue tests for the nano-silica modified materials are very noteworthy, since these increases are accompanied by significant improvements being recorded in the initial toughness.