To obtain a rare-earth sulfide of a fine grain size by heating and vaporizing a rare-earth halide in hydrogen sulfide in the presence of an alkali or aluminum halide.

The hydrogen sulfide is circulated into a reactor consisting of a first tube. The rare-earth halide and the alkali or aluminum halide are arranged within a second reactor of a tube type and a nitrogen stream is circulated therein. The second reactor is heated to 700 to 1200°C to vaporize the rare-earth halide and the alkali or aluminum halide. The vaporized matter thereof is introduced into the first reactor where the vaporized matter and the hydrogen sulfide are reacted. The rare-earth sulfide having the grain size below 1 μm is thus obtd.