Single crystals of ThO2were grown from molten Li2O· 2WO3solvent at 1225°–1300°C. Growth occurred primarily by solution transfer from ThO2nutrient at 1250°–1350°C to seeds in regions 20°–75° cooler. The resulting crystals, optically transparent octahedra up to 3 mm on edge, contain <500 ppm W and <50 ppm Li as major impurities. The method was also used to prepare ThO2crystals containing limited amounts of several lanthanide ions. Increased growth rates were obtained by adding 1 wt% B2O3to the Li2O· 2WO3solvent.