The conditions of the formation of rare earth element 3,5-dihydroxybenzoates have been studied; their quantitative composition and solubilities in water at 293 K have been determined. The IR spectra of the hydrated complexes have been recorded and their thermal decomposition in air determined. During heating, the hydrated complexes Ln(C7H5O4)O-3 . nH(2)O (n = 4 for La-Pr, n = 7 for in Y, Nd-Lu) lose water of crystallization in one step and then the anhydrous complexes decompose directly to oxides (Sm-Gd, Dy-Lu, Y) or with intermediate formation of Ln(2)O(2)CO(3)(La, Nd). The conditions of thermal decomposition of 2,4- and 3,5-dihydroxybenzoates are compared.