The study reveals that a new type of sulfidic crosslinks arising from the reaction between carboxylated nitrile:rubber (XNBR) and bis(diisopropyl)thiophosphoryl disulfide can improve the mechanical properties of the XNBR vulcanizates. The study further reveals the fact that these sulfidic crosslinks in combination with metallocarboxylate cross-links produce a significant effect in XNBR vulcanization. Some investigations have been carried out using a methyl iodide probe to elucidate the formation of chemical linkages during cure. Also, attempts have been made to establish the relationship between the structure and physical properties of the XNBR vulcanizates in this respect.