Amino-terminated hyperbranched poly(ester-amine) (HP) was prepared and used as a toughening agent for epoxy resin in presence of Montmorillonite organoclay (OMMT) as a reinforcing filler. Several parameters which affect the physico-mechanical properties of epoxy/clay nanocomposites were studied including HP content, clay concentration, and intercalation/exfoliation and degree of dispersion of OMMT clay within the epoxy matrix. The results showed a significant improvement in toughness, physico-mechanical properties and enhancement in thermal stability of epoxy/clay nanocomposites upon using HP (20 wt%) as a toughening agent at low OMMT clay loading (1 wt%). These promising results could open the way for epoxy resins to be used in more high-impact resistance applications.