Sodium metatungstate is the inorganic compound with the formula Na<sub>6</sub>[H<sub>2</sub>W<sub>12</sub>O<sub>40</sub>], sometimes written 3Na<sub>2</sub>WO<sub>4</sub>÷9WO<sub>3</sub>÷H<sub>2</sub>O. It is also referred to as sodium polytungstate (SPT). This salt has been used in the manufacture of dense aqueous solutions. Sodium metatungstate exists as white solid. The anion is the polyoxotungstate [H<sub>2</sub>W<sub>12</sub>O<sub>40</sub><nowiki>]</nowiki><sup>6-</sup>, which features six-coordinated tungsten(VI) centers interconnected with doubly- and triply bridging oxo ligands.
Due to its very high solubility in water (max. density 3.1 g/cm<sup>3</sup>), SPT is widely used as to produce "heavy liquid" for gravity separation (sink /float analysis) and density gradient centrifugation. It has significant advantages when compared to zinc chloride solution or the toxic halogenated carbons for sink-swim analysis. Aqueous SPT is non-toxic (unlike the denser Clerici solution), non-flammable, odorless, reusable and additionally it has a low viscosity.