The effect of composition and concentration of polystyrene-block-polybutadiene-block -poly-(methyl methacrylate) (SBM) copolymer triblock on final morphologies and properties of modified epoxy networks has been investigated. The DGEBA-MCDEA epoxy system, which ensures the miscibility of most of the PMMA blocks until the end of the reaction and thus the generation of a nanostructurated material, has been chosen. For low copolymer concentration (10 wt %), the network structure is found to be independent of the composition and micelles of PS and PB blocks, can be undifferently observed. However, increasing copolymer amounts from 10 to 50 wt induces a morphology change to either "spheres on spheres" or "core-shell" structure depending on the PB content in the triblock, For copolymer concentration higher than 50 wt %, the morphology strongly depends on the processing technique used, and only films prepared by solvent casting show an organization with long-range order similar to the neat block copolymer. The toughness of nanostructured epoxy networks has been evaluated. For low SBM concentration the toughness was observed to linearly vary with the PB concentration. For higher SBM concentrations (30 and 50 wt %) the "spheres on spheres" morphology is found to be more efficient than the "core-shell" one to improve the toughness of the epoxy network. But in all cases a higher toughness is obtained when the nanostructure is preserved; when a macrophase separation occurs, the toughness increase is lower.