Polypropylene/maleated (styrene-ethylene-butadiene-styrene) (PP/SEBS-g-MA) blends reinforced with 0.2-2.5 wt% carbon nanofibers (CNFs) were prepared by injection molding. The structure, thermal, mechanical, and fracture behaviors of PP/SEBS-g-MA blends and their nano-composites were studied. Wide-angle X-ray diffraction (WAXD) results showed that the SEBS-g-MA and/or CNF additions do not induce a structural change of PP. Tensile measurements showed that the Young's modulus and tensile yield strength increase with the increasing filler content. Izod impact and essential work of fracture test results demonstrated that CNFs are beneficial to improve the impact strength and specific essential work of fracture of PP/SEBS-g-MA blends. Therefore, tough PP-nanocomposites can be achieved by melt-blending low fractions of CNFs and appropriate elastomer contents. POLYM. ENG. SCI., 51:948-958,2011. (C) 2011 Society of Plastics Engineers