This study systematically investigates the influence of a Polymethylmethacrylate-block-Polybutylacrylate-block-Polymethylmethacrylate (PMMA-b-PBuA-b-PMMA) triblock copolymer (BCP) on the flexural properties, the static fracture toughness and especially the resistance to fatigue crack propagation (FCP) of a cycloaliphatic amine cured bisphenol A based epoxy resin (EP). The results show that already small concentrations of BCP can significantly improve fracture toughness and the resistance to fatigue crack propagation. Crack growth rate as well as the Paris' law exponent m were considerably reduced from m=15.5 of the neat epoxy to m=8.1 for the BCP toughened materials. Simultaneously, the resistance to fatigue crack propagation was found to increase drastically from a critical stress intensity factor range KIc of 0.39MPa to 0.81MPa. Fractography and structural analysis reveal that the improved resistance to fatigue crack propagation correlates to crack shielding and zone shielding mechanisms caused by the synergistic interaction of BCP-rich domains and dispersed nanometer sized, presumably BCP-rich particles in epoxy-rich regions. POLYM. ENG. SCI., 57:579-587, 2017. (c) 2017 Society of Plastics Engineers