Reactivities of various rubbers (SKB, SKS-30 and NR) were studied at vulcanization temperatures, employing MBTS, CBS and sulfur as vulcanizing agents. The systems, rubber plus accelerator, and rubber plus accelerator plus sulfur were subjected to such temperatures. Reactivities of the rubbers were determined by measuring the degree of dehydrogenation indicated by formation of MBT. Reactivities were also determined by the addition of RS⋅ radicals to polymer chains, the variation in maxima of gelling and the kinetics of addition of elementary sulfur. Dehydrogenation resulting from addition of accelerator radicals to polymer chains in the rubbers assumed the following order: SKB > SKS-30 > NR. Reactivity of elementary sulfur to rubbers, in the presence of the accelerators employed, assumed the reverse order; NR > SKS-30 > SKB. The differences in the reactivities of the various rubbers is associated with the peculiarities of their structures.