The decomposition of hydrogen sulfide to hydrogen and sulfur on a variety of transition metal sulfides has been studied in a flow system at 400–800°C. Hydrogen yields were measured as a function of temperature in order to compare the effectiveness of the metal sulfides in promoting the decomposition. For the series Cr 2S 3, MoS 2, WS 2 it was found that MoS 2 is the most effective catalyst above 600°C but both Cr 2S 3 and WS 2 gave higher H 2 yields than MoS 2 below 600°C. For the group of metal disulfides FeS 2, CoS 2 and NiS 2, thermal decomposition of MS 2 to non-stoichiometric metal sulfides starts at ca. 550°C. The monosulfides FeS, CoS and NiS produce high yields of hydrogen initially due to sulfidation of the solid phase by H 2S to give the same non-stoichiometric sulfides which, themselves, are not good catalysts for the thermal decomposition of H 2S. The copper sulfides Cu 2S, Cu 9S 5. CuS were not effective catalysts for the thermal decomposition of H 2S.