The influence of dimethyl disulfide (DMDS), which is widely used as an additive in ethylene plants, on coke formation during the steam cracking of hydrocarbons was investigated in a continuous-flow stirred-tank reactor (CSTR) setup with n-hexane as the feed and in a pilot-plant setup with ethane as the feed. Both of the reactors were made of Incoloy 800HT. Experiments were carried out at conditions relevant to industrial steam crackers. DMDS was applied by presulfidation, continuous addition, and presulfidation followed by continuous addition. Application of DMDS suppresses CO production. The influence of DMDS on coke formation was found to depend on the application method and the amount of DMDS used. SEM examination of the coke samples obtained from the steam cracking of n-hexane indicated that application of DMDS leads to a significant change in the coke morphology. EDX analysis indicated that application of DMDS causes a significant change in the metal content and distribution in both the alloy surface and the coke layers. The mechanism of the influence of DMDS on the coke formation is discussed.