The morphology of nylon 6/polypropylene blends modified with maleated rubbers, such as styrene-ethylene/butylene-styrene triblock copolymers (SEBS-g-maleic anhydride (MA)) and ethylene-propylene random copolymers (EPR-g-MA), is affected by changes in the level of functionality of the rubber. By adjusting this level of functionality it is possible to induce drastic changes in the morphology of blends with fixed composition. Unfunctionalized versions of these elastomers are difficult to disperse in the nylon 6 phase, even in the presence of maleic anhydride-polypropylene, and lead to blends with low toughness. The use of polypropylene (PP) grafted with maleic anhydride (PP-g-MA.) in addition to the maleated rubbers improves the degree of dispersion of the polypropylene phase and the low temperature toughness of the blends. Blends with up to 16% PP-g-MA showed ductile-brittle transition temperatures as low as the transition temperature of toughened nylon 6 (-30 degrees C). The degree of heterogeneity of mixtures of PP and PP-g-MA has a profound effect on the low temperature toughness and morphology of the rubber-modified nylon 6/PP blends, particularly in blends with compositions in the transition region of phase continuity. A fine degree of dispersion of the PP-g-MA in PP is desired in these mixtures, since it leads to the best low temperature toughness in blends of fixed composition.