A new simple metathetical sulfidation method using boron sulfides has been developed to prepare nanoparticles of NdS2 via conversion of ca. 50-nm-sized nanoparticles of Nd2O3 at 450 degreesC, in which boron and sulfur powders form boron sulfides in situ and evaporate to sulfidize the oxide. The X-ray powder diffraction analysis revealed that the products were purely NdS2, and the atomic absorption spectrometric analysis confirmed nonexistence of boron in the products after washing with water. The detailed TEM studies showed that the NdS2 nanoparticles maintained the original size of the oxide particles without fusion during the low-temperature sulfidation process.