A polymer blend consisting of nylon 6 and ethylene-vinyl acetate copolymer (,EVA) was compatibilized with an ethylene-acrylic acid copolymer (EAA). Neither EVA nor EAA are compatible with nylon 6; however, the combination of the two resulted in a toughened nylon 6. The compatibilization was revealed by the dramatic increase in impact strength, and the smaller particle size and finer dispersion of EVA in the nylon 6 matrix in the presence of EAA. The degree of toughening was evaluated through its effect on the mechanical, morphological and rheological properties, by changing the proportion of the components in the nylon 6/EVA/EAA blends. Because EAA is a compatibilizer for nylon 6/EVA and EVA a compatibilizer for nylon 6/EAA, both the toughening and the compatibilization are cooperative.