In this work, the beta-nucleated isotactic polypropylene (iPP)/ ethylene-octene copolymer (POE) blends demonstrated greatly enhanced impact toughness by adding traces of carbon nanotubes (CNTs) (only 0.05 wt%). When the POE content was 30 wt%, the impact strength of beta-nucleated iPP/POE blends with CNTs was as high as 51.7 kJ/m(2), about 5.6 kJ/m(2) higher than beta-nucleated iPP/POE blends, 15.2 kJ/m(2) higher than CNTs-filled iPP/POE blends, and almost 19 times of pure iPP sample. This significantly improved impact toughness was considered to be attributed to the shear yielding and multiple-crazing, originating from the presence of abundant beta-crystals in the iPP matrix, the enhanced mobility of the molecular chains in the confined amorphous region of iPP lamellae and the homogenous distribution of POE dispersed phase with a small size, indicating the synergistic effect of CNTs, beta-nucleating agent and POE on the toughness of iPP. POLYM. ENG. SCI., 59:757-764, 2019. (c) 2018 Society of Plastics Engineers