Mercapto-modified ethylene-vinyl acetate (EVASH) has been employed as a reactive compatibilizing agent for nitrile-butadiene rubber (NBR)/ethylene-propylene-diene monomer (EPDM) blends vulcanized with a sulfur /2,2'-dithiobisbenzothiazole (MBTS) single accelerator system and a (sulfur/MBTS/tetramethylthiuram disulfide (TMTD) binary accelerator system. The addition of 5.0 phr EVASH resulted in a significant improvement in the tensile properties of blends vulcanized with the sulfur/ MBTS system. In addition to better mechanical performance, these functionalized copolymers gave rise to a more homogeneous morphology and, in some cases, better aging resistance. The compatibilization. was not efficient in blends vulcanized with the S/MBTS/TMTD binary system, probably because of the faster vulcanization process occurring in this system. The good performance of these EVASH samples as compatibilizing agents for NBR/EPDM blends is attributed to the higher polarity of these components that is associated with their lower viscosity. Dynamic mechanical analysis also suggested a good interaction between the phases in the presence of EVASH. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1404-1412, 2004.