Li2S is a critical raw material for next-generation secondary batteriesNext-generation secondary batteries. This study investigates an efficient method for producing Li2S via the reaction of H2S gas with either LiOH or Li2SO4. In the experiments, H2S gas was generated by dissolving FeS in a H2SO4 solution at 298 K, and then reacted with LiOH at 673 K or with Li2SO4 at 1073 K. Experimental results showed that LiOH was converted to Li2S at 673 K by reacting with H2S gas, and elemental S was condensed at the low-temperature part of a reactor owing to H2S decomposition. Meanwhile, Li2SO4 was converted to Li2S at 1073 K by reacting with H2S gas under high pS2 conditions, driven by both H2S decomposition and a side reaction between SO2 and H2S gas. These results demonstrated the feasibility of producing high-purity Li2S from LiOH and Li2SO4 using H2S gas.