The morphological and rheological behaviors of toughened epoxy resins modified with core-shell rubber particles (CSR) were studied. These rubber particles were based on a poly (butadiene-co-styrene) core and a crosslinked poly (methyl methacrylate) shell. The effect of functionalized groups was performed on two types of CSR particles: first, those containing carboxyl-functionalized groups (CSf), and second, particles containing no carboxyl-functionalized groups (CSnf) in the PMMA-shell. For these blends, the correlations between the morphology, particle dispersion state and their rheological behaviors before curing were investigated. Preliminary work using TEM micrographs indicated that the blends modified with CSf and CSnf exhibited the same particle size but differed with respect to the dispersion state. Rheological behavior of these blends was assessed in steady shear flow and dynamic viscoelastic experiments. Yield viscosity near-zero shear rate occurred in the DGEBA/CSf blend presenting non-Newtonian behavior at the particle volume fraction of 20% vol. The rheological behavior was clearly related to the state of particle dispersion and analyzed taking into account interactions between the particles-particles and the particles-matrix. The Williams-Landel-Ferry (WLF) shift procedure was used to construct modulus master curves G' and G" from the elastic solid state to molten polymers. A secondary plateau existed at low frequencies and was related to the presence of interactions leading to a physical network-type structure. The deviation between theoretical G' (Palierne's model) and experimental G' values was evaluated and exhibited high elasticity at the terminal zone, which correlated well with available literature.