The basic steps in the reaction of Nd-2(SO4)(3) with CS2 were studied by thermogravimetric techniques to elucidate the reaction mechanism of the formation of Nd2S3. The Nd-2(SO4)(3) first decomposes to Nd2O2SO4 in the range 500-650 degrees C, depending on the heating rate. Nd2O2SO4 is further deoxygenated to Nd2O2S, which forms a disulfide phase at lower temperatures (500-600 degrees C) by reaction with CS2. Neodymium disulfide, which exhibits a wide range of non-stoichiometry (NdS1.876-NdS2), decomposes into Nd2S3 above 600 degrees C. At lower heating rates (1 and 5 degrees C min(-1)), orthorhombic Nd2S3 is formed in a single phase on heating to 1100 degrees C. In contrast, non-stoichiometric cubic Nd2S3-x is formed together with orthorhombic Nd2S3 when the heating rate is as high as 10 degrees C min(-1).