An investigation was conducted to characterize fracture behaviours of nano-silica modified epoxies at low and elevated temperatures. A nanosilica dispersed epoxy ( Nanopox XP 22/0516, Hanse-Chemie, Germany) with 40 wt% silica nano-particles was used as modifier to toughen an epoxy resin, Araldite F ( Bisphenol A based, Ciba-Geigy). Fracture toughness and other mechanical properties were measured using standard compact tension (CT), tensile and flexural specimens to elaborate the effects of nanosilica particles on fracture behaviours of epoxy nanocomposites at different temperatures, -50, 0, 23, 50 and 70 degrees C. Dynamic mechanical analysis (DMA) was utilized to define the glass transition temperature (Tg) upon the addition of different amounts of nanosilica particles. Fracture toughness of the nano-silica modified epoxies was clearly increased at 23 degrees C and 50 degrees C, but the role of nano-silica particles in enhancing the fracture toughness became less pronounced at 0 degrees C and -50 degrees C and disappeared at 70 degrees C.