The pyrolysis of hydrogen sulfide has been studied at residence times between 0.4 and 1.6 s and in the temperature range of 800−1100 °C. A continuous perfectly mixed quartz reactor was used to acquire kinetic data on the thermal dissociation of hydrogen sulfide and elemental sulfur mixtures diluted in argon (95 vol %). The kinetic auto-acceleration effect of sulfur is demonstrated. A detailed radical mechanism is written to account for the experimental results, in particular for the auto-acceleration effect, and validated against experimental results. This pyrolysis kinetic scheme is the first step and core of a complete detailed mechanism capable of modeling the various oxidation reactions encountered in an industrial Claus furnace.