New polymer blends of polypropylene random copolymer (PP-R) and poly(ethylene-octene) (POE) were prepared by melt-blending process using a corotating twin-screw extruder. The POE content was varied up to 35%. The toughening efficiency of POE for PP-R was evaluated by the mechanical properties of the resulted PP-R/POE blends. The crystallization behavior and morphology of the blends were also studied. Results show that POE acts as nucleation agent to induce the crystallization of PP-R matrix at higher crystallization temperature. Super-toughened PP-R/POE blends (Izod impact strength more than 500 J/m) can be readily achieved with only 10 wt % of POE. The high toughness of PP-R/POE is attributed to cavitation and shear yielding of matrix PP-R, as revealed by the morphology studies. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 461-468, 2011