A 2-thiobenzothiazole/p-phenylenediamine vulcanization intermediate has been characterized by means of ultra-high-performance liquid chromatography–tandem quadrupole time-of-flight mass spectrometry. Pregenerated 2-thiobenzothiazole/p-phenylenediamine intermediate has a clear effect on accelerating the sulfur crosslinking reaction. Therefore, the generation of vulcanization active species can act as a proof that p-phenylenediamine antioxidant could exert an influence on the vulcanization process via a reaction with the accelerator. Based on an analysis of samples from different curing stages, it is speculated that the intermediate is most likely generated in the vulcanization induction period. This research also provides indirect evidence of the effect of zinc oxide on vulcanization. The intermediate can be detected in both solution and vulcanizate. Its formation is likely to be a zinc ion–mediated reversible mechanism involving a radical course.