Polychloroprene is a diene rubber, but unlike other diene rubbers, its compounding with various additives and curing mechanisms is different. A derivative of thiourea, ethylene thiourea (ETU), is widely used to vulcanize chloroprene rubber (CR), and the vulcanizates thus obtained exhibit excellent mechanical properties, good aging resistance, and very good sealing properties. However, the problem is that ETU is reported to be a potent carcinogenic compound, and hence, the effective substitution for ETU has been extensively explored. In this study, we used a naturally occurring amino acid derivative, dimethyl L-cystine, as an ecofriendly compound for the vulcanization of CR. It had a significant influence on the curing characteristics and mechanical properties, such as modulus, tensile strength, elongation at break, and hardness values. The concentration of this novel crosslinking agent and also the curing temperature were optimized. In the presence of dimethyl L-cystine, the amount and activity of magnesium oxide also exhibited significant influences on the crosslinking characteristics.