AbstractTetramethylthiuram disulfide‐accelerated sulfur vulcanization of natural rubber has been investigated. Continuous measurements in a Vuremo curemeter at 145°C were used to estimate the effects of zinc oxide concentration on the induction periods, on the first‐order rate constants, and on the ultimate extents of crosslinking, on the extents of degradation reaction (reversion), and on the extents of relaxation of vulcanizates at the cure temperature. The concentration of zinc oxide has practically no influence on the rate of thiuram‐accelerated sulfur cure. The values of the ultimate extents of crosslinking increase with increasing the zinc oxide content in the rubber compound up to a certain limit corresponding to the theoretical amount of zinc oxide which is necessary for the formation of zinc dimethyldithiocarbamate from tetramethylthiuram disulfide and zinc oxide during the vulcanization reaction. From the point of view of the reversion, however, this limit value of zinc oxide concentration is not sufficient. The relaxation measurements provide the same results. On the basis of these, for thiuram‐accelerated sulfur vulcanizations, the optimum zinc oxide content in the rubber mix of 2.5 phr has been calculated. This value is in very good agreement with the optimum value of zinc oxide concentration found for both sulfenamides and thiazoles‐accelerated su