In the present work, the effectiveness of using a styrene/ ethylene-butylene/styrene rubber grafted with maleic anhydride (MA) as toughening material in ternary blends with two polyamide-6 nanocomposites or PP with different molecular weight as matrix phases was evaluated in terms of SEM and TEM morphology, WAXD, capillary rheometry, and tensile properties determination. Two metallocene polyethylenes and two polypropylenes were used as the dispersed phase in these ternary blends, and the effect of the comonomer contents in the former was also evaluated. Results showed that the blends prepared with metallocene polyethylenes are tougher than those prepared with PP as the dispersed phase and no significant changes in the Young's modulus or tensile strength were observed when changing the type of metallocene polyethylenes used. When a blend of SEBS/SEBS-g-MA instead of SEBS-g-MA alone was used as a compatibilizing agent in the ternary PA-6 nanocomposite blends, a major decrease in the Young's modulus and tensile strength and a higher toughness were observed. The formation of PA-OMMT particle clusters seems to improve the toughness/stiffness balance. These results are related to the degree of clay dispersion in the polyamide and to the type of morphology developed in the different blends. POLYM. ENG. SCI., 46:1111-1120, 2006.