Alumina nano-crystals were dispersed in epoxy resin via different approaches. The effects of filler dispersion on the mechanical properties of the epoxy/alumina nanocomposites were studied. The fracture mechanisms are investigated using SEM. The results show that the Young’s modulus, tensile strength, elongation at break and fracture toughness of epoxy were improved dramatically with the incorporation of well-dispersed alumina nano-crystals. The poorly-dispersed nano-crystals, however, showed little effects on the mechanical properties.