The covulcanization characteristics, mechanical properties, compatibility, and hot-air aging resistance of hydrogenated nitrile-butadiene rubber (HNBR)/ethylene-propylene-diene rubber (EPDM) blends cured with either sulfur or dicumyl peroxide (DCP) were studied. The difference between MH and ML (MH - ML), rheometer graphs, selective swelling and a dynamic mechanical analysis of HNBR/EPDM blends confirmed that the peroxide curing system gives better covulcanization characteristics than the sulfur curing system and peroxide exhibited higher crosslink efficiency on EPDM while sulfur showed larger crosslink efficiency on HNBR. Dynamic mechanical analysis and morphology indicated that the compatibility between HNBR and EPDM is limited. Tensile strength and elongation at break of the sulfur-cured blends are greater than those obtained with peroxide and increase with the HNBR fraction. The blends crosslinked with peroxide retain their tensile strength but not their elongation at break after hot air ageing better than blends vulcanized by sulfur. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013