A prolonged crystallization of samarium sulfite solution at 70 degrees C yields a disulfite sulfate hydrate precipitate Sm-2(SO3)(2)SO4 . nH(2)O, where it is approximate to 2.5. The solid phase was characterized by X-ray powder diffraction, thermal analysis (TG, DTG and DTA) and IR spectroscopy. TG measurements revealed dehydration at 150-300 degrees C and then a complex decomposition between 300 and 900 degrees C leading in both air and argon to oxosulfate Sm2O2SO4.