The possibility of sulfide synthesis by carbon reduction of neodymium sulfate was studied by the thermogravimetric technique. Anhydrous Nd,(SO,), was formed by heating Nd-2(SO4)(3) . 8H(2)O in vacuum or in air at 300 degrees C. When Nd-2(SO4)(3) was mixed with annealed carbon and heated in nitrogen, neodymium oxysulfide Nd2O2S was formed at 880 degrees C. However, when Nd-2(SO4)(3) was mixed with activated carbon, the products after heating at the same temperature comprised a mixture of neodymium sulfide Nd3S4 with Nd2O2S. The ratio of Nd3S4 to Nd2O2S was found to vary with the reaction conditions.