It is well known that the use of binary accelerator systems in rubber vulcanization provide better physical and chemical properties to the vulcanizates. The present work reports the results obtained on the study of amidinothiourea as a secondary accelerator along with tetramethyl thiuram disulfide (TMTD) in the sulfur vulcanization of natural rubber. Vulcanizates containing amidinothiourea have an appreciable increase in mechanical properties and better retention of these properties after aging compared to the reference mixes used. These mixes containing amidinothiourea showed appreciable reduction in optimum cure time as well. This suggests a nucleophilic reaction mechanism in the vulcanization reactions under review. Mixes with varying concentrations of amidinothiourea were tried; and the optimum level of amidinothiourea required has been derived based on the cure characteristics of the mixes and physical properties of the vulcanizates.