Solubilities of MgSO3.6H(2)O in water were determined in the temperature range from 43 to 94 degrees C where this hydrate is metastable. Solubilities of MgSO3.6H(2)O and MgSO3.3H(2)O in an aqueous solution containing 150 g of MgSO4/L were determined from 30 to 95 degrees C.