The catalytic oxidation of hydrogen sulfide into sulfur with molecular oxygen has been studied in the temperature range 130–200 °C. Active carbon, molecular sieve 13X and liquid sulfur were used as catalysts. Sulfur is adsorbed in the micropores (3 < r < 40 Å) of the catalysts. Experiments with a surface of liquid sulfur demonstrated that sulfur is a catalyst for H2S oxidation. This catalytic function reflects itself in the fact that H2S oxidation rate showed a maximum as a function of the amount of sulfur present in the pores of active carbon and molecular sieve 13X. The kinetics of the reaction and the activation energy are equal on catalysts of different chemical composition. The mechanism of the catalysis by sulfur is discussed as well as the function of traces of iron oxide, present in most catalysts.