The synergistic toughening effect of nucleating agent (NA) and ethylene-octene copolymer (POE) on polypropylene was studied in the present work. Two different nucleating agents, such as a-form nucleating agent 1,3 :2,4-bis (3,4-dimethylbenzylidene) sorbitol (DMDBS, Millad 3988) and P-form nucleating agent aryl amides compounds (TMB-5), were selected to blend with PP or PP/POE blends, respectively. The results show that PP containing 0.5-0.25 wt % DMDBS or 0.5-0.25 wt % TMB-5 has relatively low impact strength. For PP/POE blends, although the impact strength increases gradually with the increasing of POE content, high content of POE is needed to obtain the available PP toughness. However, once nucleating agent and POE are simultaneously added into PP, PP/POE/NA blends show great improvement of toughness even at low POE content. Furthermore, the synergistic toughening effect of POE/TMB-5 is more apparent than that of POE/DMDBS. SEM results show that whether DMDBS or TMB-5 has no apparent effect on the morphologies of POE in the PP/POE/NA blends. Further investigations using DSC and POM indicate that both DMDBS and TMB-5 induce the apparent enhancement of the crystallization temperature of PP and the sharp decrease of spherulites size of PP in the PP/POE/NA blends. The possible synergistic toughening mechanism is discussed in the work. (C) 2008 Wiley Periodicals, Inc.