二氧化钍，别名氧化钍，化学式ThO₂。

硝酸钍溶液与草酸溶液反应沉淀出草酸钍。经过滤、洗涤、干燥，并在650～800°C下灼烧，制得二氧化钍。

Thorium dioxide (ThO₂), also called thorium (IV) oxide, is a crystalline solid, often white or yellow in color. It was formerly known as thoria. It is produced mainly as a by-product of lanthanide and uranium production. Thorianite is the name of the mineralogical form of thorium dioxide. It is moderately rare and crystallizes in isometric system. The melting point of thorium oxide is 3300 °C – the highest of all known oxides. Only a few elements (including tungsten and carbon) and a few compounds (including tantalum carbide) have higher melting points.