The compatibilizing effect of mercapto-modified ethylene-vinyl acetate (EVALSH) was investigated in vulcanized nitrile rubber (NBR)/ethylene-vinyl acetate (EVA) copolymer blends. EVALSH increased the ultimate tensile strength, mainly in blends containing larger amounts of NBR. In addition, an accelerating effect of this functionalized copolymer was observed in blends vulcanized with the sulfur system. This behavior was confirmed with oscillating disk rheometry and differential scanning calorimetry analyses. The improvement of the mechanical performance was attributed to the interfacial action associated with the increase in the crosslink density of the NBR phase promoted by the mercapto groups in EVALSH. The effects of EVALSH on the morphology and dynamic mechanical properties were also studied. (C) 2003 Wiley Periodicals, Inc.