A new polymorph of Sm-2(SO3)(3) . 3H(2)O (beta-form) has been synthesized and its properties are compared to those of the previously known alpha-form. The polymorphs have been characterized by X-ray diffractometry, FTIR spectroscopy and thermal analysis. The thermoanalytical studies, particularly by simultaneous TG and DTA, as well as by EGA with both MS and FTIR detection, show distinct differences between the two phases.