Magnesium sulfite is the magnesium salt of sulfurous acid with the formula . Its most common hydrated form has 6 water molecules making it a hexahydrate, ÷6. When heated above , it is dehydrated to magnesium sulfite trihydrate, or ÷3. The anhydrous form is hygroscopic, meaning that it readily absorbs water from the air.
Solubility tables of MgSO<sub>3</sub>