Ethylene-propylene-diene with ethylene norbornene as the diene (EPDM) samples functionalized with thioacetate (EPDMTA) or mercapto groups (EPDMSH) were employed as compatibilizing agents for nitrile rubber (NBR)/EPDM blends. The cure rate of the blend was affected by the presence of a small portion of these compounds. EPDMTA decreases the cure rate of the blends, whereas EPDMSH was able to decrease the scorch time and increase the cure rate when employed in a proportion as high as 5.0 phr. The compatibilization effect was influenced by the nature of the EPDM employed in the blends. Blends consisting of an EPDM sample with lower viscosity display better dispersion of the EPDM phase inside the NBR matrix and also better mechanical performance with the compatibilization. The compatibilization with EPDMSH is reactive, with the formation of chemical bond between the mercapto groups of the compatibilizing agent and the double bond of the diene rubber. The compatibilization with EPDMTA is also considered to be reactive because the vulcanized blends containing this functionalized copolymer contain a higher amount of cross linked material, as indicated by the lower weight loss after swelling experiments. A scanning electron micrograph demonstrated that these functionalized copolymers led to a filler phase morphology, mainly in NBR/EPDM57C blends. The compatibilization increases the dynamic elastic modulus without affecting the damping. An improvement of thermal aging resistance of the studied blends was also achieved with the presence of the functionalized copolymers.