Disodium hydrogen arsenate is the inorganic compound with the formula Na2HAsO4.7H2O.

The compound consists of a salt and seven molecules of water of crystallization although for simplicity the formula usually omits the water component.

Disodium hydrogen arsenate is highly toxic.

The salt is the conjugate base of arsenic acid.

[1] Being a diprotic acid, its acid-base properties is described by two equilibria: This inorganic compound–related article is a stub.