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In the past decade extensive studies have been focused on mechanical properties of inorganic nanofiller/epoxy matrices. In this work we systematically investigated the mechanical properties of nano-alumina-filledE-54/4,4-diaminodiphenylsulphone(DDS)epoxyresins,whichwereprepared via combining high-speed mixing with three-roll milling. Homogeneous dispersion of nano-alumina withsmallagglomerateswasobtainedinepoxyresin,whichwasconfirmedusingtransmission electronmicroscopy(TEM).Thestatic/dynamicmodulus,tensilestrengthandfracturetoughness of the nanocomposites were found to be simultaneously enhanced with addition of nano-alumina fillers. About 50% and 80% increases of KIC and GIC were achieved in nanocomposite filled with 18.4wt%aluminananofillers,ascomparedtothatoftheunfilledepoxyresin.Furthermore,the corresponding fracture surfaces of tensile and compact tension samples were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques in order to identify the relevant fracture mechanisms involved. Various fracture features including cavities/debonding of nanofiller,localplasticdeformationaswellascrackpinning/deflectionwerefoundtobeoperative in the presence of nano-alumina fillers.