The thermal decomposition in air of 2,5-dichloribenzoates of rare earth elements (Y, La-Lu, without Pm) has been studied. During heating, the hydrated complexes Lu(C7H3Cl2O3) . nH2O (n = 2, 4, 8) decompose in three steps, with the exception of cerium, which decomposes in two steps. The hydrated complexes heated lose all (Y, Gd) or some molecules of water of crystallization (La, Pr-Eu, Tb-Tm) and next decompose to the oxides with intermediate formation of LnOCl, except Ce(III) complex which decomposes directly to CeO2. The anhydrous complexes of Yb and Lu decompose in two steps to the oxides with intermediate formation LnOCl.