Sodium manganate is the inorganic compound with the formula Na<sub>2</sub>MnO<sub>4</sub>. This deep green solid is a rarely encountered analogue of the related salt K<sub>2</sub>MnO<sub>4</sub>. Sodium manganate is rare because it cannot be readily prepared from the oxidation of manganese dioxide and sodium hydroxide. Instead this oxidation reaction tends to stop at producing sodium hypomanganate, Na<sub>3</sub>MnO<sub>4</sub>, and even this Mn(V) salt is unstable in solution. Sodium manganate can be produced by reduction of sodium permanganate under basic conditions:
Because NaMnO<sub>4</sub> is difficult to prepare, sodium permanganate is more expensive than potassium permanganate.