Lutetium(III) chloride or lutetium trichloride is the chemical compound composed of lutetium and chlorine with the formula LuCl<sub>3</sub>. It forms hygroscopic white monoclinic crystals and also a hygroscopic hexahydrate LuCl<sub>3</sub>÷6H<sub>2</sub>O. Anhydrous lutetium(III) chloride has the YCl<sub>3</sub> (AlCl<sub>3</sub>) layer structure with octahedral lutetium ions. Its isotopologue lutetium (<sup>177</sup>Lu) chloride is used as a radioactive tracer for diagnosis and/or treatment in anti-cancer therapies.
Pure lutetium metal can be produced from lutetium(III) chloride by heating it together with elemental calcium: