A thermoplastic polyolefin (TPO) containing 70 wt % styrene-ethylene-butadiene-styrene-g-maleic anhydride and 30 wt % polypropylene and its nanocomposites reinforced with 0.3-1.5 wt % organoclay were prepared by melt mixing followed by injection molding. The mechanical and fracture behaviors of the TPO/clay nanocomposites were investigated. The essential work of fracture (EWF) approach was used to evaluate the tensile fracture behavior of the nanocomposites toughened with elastomer. Tensile tests showed that the stiffness and tensile strength of TPO was enhanced by the addition of low loading levels of organically modified montmorillonite. EWF measurements revealed that the fracture toughness of the TPO/clay nanocomposites increased with increasing clay content. The organoclay toughened the TPO matrix of the nanocomposites effectively. (c) 2008 Wiley Periodicals, Inc.