The reactive compatibilization of ethylene-propylene-diene (EPDM)-nitrile rubber (NBR) blends has been performed using both EPDM and EVA functionalized with mercapto or maleic anhydride groups. The mechanical properties of NBR/EPDM (70:30 wt%) blends were significantly improved with the addition of 5 phr of mercapto-functionalized EVA (EVASH). The mercapto groups were able to react with the double bonds of the high diene rubber, resulting in a good interaction between phases. However, mercapto-modified EPDM (EPDMSH) was not efficient as compatibilizing agent. The best results achieved with EVASH may be attributed to the higher polarity of this component associated to its lower viscosity. An additional improvement on mechanical properties was also observed when EVASH is used in combination with nitrile rubber functionalized with epoxy or oxazoline groups. EVA copolymer functionalized with maleic anhydride displayed similar results. Dynamic mechanical analysis confirmed the efficiency of the reactive compatibilization. A substantial broadening of the tan 6 curves related to the NBR transition and a shift towards lower temperature have been observed with the presence of the co-reactive functional copolymers based on EVASH and NBR functionalized with epoxy or oxazoline groups.