Variation of dynamic mechanical properties like storage modulus (E’) and loss tangent (tan delta) with temperature show the presence of two transitions in the carboxylated nitrile rubber (XNBR) molded in the presence of zinc oxide (ZnO). The low-temperature transition is due to the glass-rubber transition (T-g) of XNBR, and the high-temperature transition is due to formation of ionic clusters. Incorporation of reinforcing silica filler makes the high-temperature transition more prominent and high filler loading causes a shift of the transition temperature to the higher side. It is believed that the rubber-filler interaction in the cluster region causes striking changes in the variation of E’ and tan delta with a double-strain amplitude (DSA).