Iron group metal sulfides were synthesized from the elements under hydrothermal condition. For nickel sulfides, two kinds of nickel metal powder, coarse powder passed through 63 μm mesh and fine powder passed through 3 μm mesh, were used as the starting materials. The reaction with the coarse Ni powder gave NiS with appreciable amount of Ni, Ni₃S₂, and Ni₉S₈. Pure NiS was obtained by the reaction with the fine Ni powder at 240°C for 10 h. The lowest nickel sulfide Ni₃S₂ was obtained as a single phase product of the reaction if the coarse Ni powder was used. From these results, the fine and coarse powders were found to be suitable for the syntheses of NiS and Ni₃S₂, respectively. The lowest cobalt sulfide Co₉S₈ was obtained almost as a single phase though the XRD pattern of the product showed some unidentified peaks. Pure Co₉S₈ was obtained by washing the reaction product with HNO₃. In the Fe-S system, FeS was obtained with a small amount of Fe₃O₄.