A toughened-epoxy polymer based on diglycidylether of bisphenol A (DGEBA) cured with ethylenediamine (EDA) and modified with a rubber based on an epoxy-terminated acrylonitrile-butadiene random copolymer (ETBN), exhibited different morphologies depending on the rubber content. Up to 10% rubber, the morphology consisted of a random dispersion of spherical domains rich in rubber, while at 15% rubber, large and irregular domains were present, turning into a co-continuous structure at 20% rubber. Mechanical properties (elastic modulus, uniaxial compression yield stress, critical stress intensity factor, K(IC) and strain energy release rate, G(IC)) of the toughened epoxies and hybrid-particulate materials containing glass beads, were analysed. The best mechanical properties were exhibited by hybrids with a random dispersion of rubbery domains in the epoxy matrix. The presence of large and irregular domains or co-continuous structures led to materials with poor mechanical properties.