Disodium hydrogen phosphite is the name for inorganic compounds with the formula Na2HPO3•(H2O)x.

The commonly encountered salt is the pentahydrate.

[1] A derivative of phosphorous acid (HP(O)(OH)2), it contains the anion HPO32−.

However, this name is misleading as the hydrogen atom is not acidic, being bonded to phosphorus rather than oxygen.

It is white or colorless solid, and is little studied.