氧化铥是一种无机化合物，化学式为Tm₂O₃。

灰白色有热色性粉末，加热后变为有光泽的红色，长时间加热则转变为黄白色。不溶于水，但能缓慢溶于强酸之中。

Thulium (III) oxide is a pale green solid compound, with the formula Tm₂O₃. It was first isolated in 1878 from an impure sample of erbia by Per Teodor Cleve, who named it thulia. It can be prepared in the laboratory by burning thulium metal in air, or by decomposition of their oxoacid salts, such as thulium nitrate.