[en] A sol-gel process for producing ThO₂ microspheres has been studied on an laboratory scale. The process consists of the following steps: source ThO₂ sol preparation by partially neutralizing Th(NO₃)₄ solution by adding NH₄OH, external gelation of ThO₂ sol drops without organic polymer additive in ammoniac hexone and conc. NH₄OH, washing, then drying and sintering. The optimum conditions for crack-free microsphere production were established. Especially, crack-free gelation was found to be achieved by using ThO₂ sols prepared under pH control, which is high in colloid particle fraction, and by quickly solidifying surface of the sol drops in hexone with high ammonia concentration. In addition, density of sintered ThO₂ microspheres was found to depend on sol properties, washing temperature and drying conditions. (author)