The present work investigates the modification of epoxy resin by using a combination of nanoclay (montmorillonite-Cloisite 30B) and a liquid polymeric modifier (polyurethane). Polyurethane was obtained from 4,4'-diphenylmethane diisocyanate and polydiols with different molecular weight: polyethylene glycol (PEG 400) and polyoxypropylene diols with molecular weight 1000 g/mol and 2000 g/mol. The impact strength, the critical stress intensity factor as well as the flexural strength were evaluated as functions of modifiers content. The obtained results showed that hybrid composites exhibit enhanced mechanical properties without significant changes of the glass transition temperature. FTIR analysis showed that chemical reactions took place between the hydroxyl groups of epoxy resin and the isocyanate groups of polyurethane, explaining an improvement of the mechanical properties of epoxy resin. However, XRD results demonstrated the formation of an exfoliated structure for the hybrid compositions with both polyurethane and montmorillonite. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3237-3247, 2011