Toughened thermosetting polymers are basis for many commercially important structural adhesives and composites systems. Several approaches have been employed to improve the fracture behavior of epoxies including the use of elastomers, thermoplastics and nanoclays. The mechanical properties of the hybrid nanocomposites depends on the morphology, crosslinking density and exfoliation degree. In this work, we proposed to study the effect of the addition of different organically treated montmorillonita clays on the network formations and phase separation of an epoxy-polysulfone (PSF) blend. The epoxy system was based on diglycidyl ether of bisphenol A and diamino diphenyl sulfone. The thermoplastic modifier was polysulfone of Mn=26,000 g/mol, varying the PSF concentration (5, 10 and 15 phr PSF). The clays used were Nanomer I.30E (NI30E), Nanomer I.28E (NI28E), Cloisite 15A (C15A) and Cloisite 10A (C10A). The curing reaction was followed by differential scanning calorimetry. The hybrid nanocomposites were characterized by dynamical mechanical analysis and scanning electron microscopy. The presence of NI30E accelerates the curing reaction, decreases the glass transition temperature (Tg) and increases the PSF domain size. On the other hand, there is a negligible change on the curing reaction and blend morphology for NI28E, C10A and C15A modified systems.