The rare earth element methylsuccinates were prepared as crystalline solids with general formula Ln2(C5H8O4 )3_nH2O, where n = 8 forCe - Nd and Tb, n = 7, for Sm, n = 6 forY andLa, n = 5 forDy - Tm, n = 4 for Eu,Yb and Lu, n = 3 forGd.The IRspectra of the complexes prepared were recorded and their solubility in water at 293 K and thermal decomposition in air atmosphere were investigated. During heating the complexes lose crystallization water in one (La, Nd - Gd, Tm - Lu) or two steps (Eu, Dy, Ho, Er) going over to monohydrates (Y, Ce, Tb) or anhydrous compounds (La, Pr - Gd, Dy - Lu) and then the complexes decompose directly to oxides (Ce, Pr, Tb - Er) or with intermediate formation of oxocarbonates Ln2O2CO3 (La, Nd - Gd) or Ln2O(CO3)2 (Y, Tm - Lu). The carboxylate groups in the complexes prepared act probably as bidentate chelating.