Sodium bisulfate is a sodium salt with the chemical formula NaHSO₄. Chemically, it is an acid salt. As opposed to neutral salts formed in acid-base neutralization reactions, acid salts are salts formed by partial neutralization of acids, which leaves one or more hydrogen atoms intact. As can be guessed from the name and the formula, it is formed by the partial neutralization of sulfuric acid (H₂SO₄) by a sodium compound such as sodium hydroxide (NaOH) or sodium chloride (NaCl).

Sodium bisulfate is a white powder. The monohydrate form is granular, whereas the anhydrous form is a hygroscopic amorphous powder. However, it is not violently hygroscopic like phosphorus compounds, and the property doesn't become a significant hindrance in its storage and transport.