In chemistry, antimonite refers to a salt of antimony(III), such as NaSb(OH)<sub>4</sub> and NaSbO<sub>2</sub> (meta-antimonite), which can be prepared by reacting alkali with antimony trioxide, Sb<sub>2</sub>O<sub>3</sub>. These are formally salts of antimonous acid, Sb(OH)<sub>3</sub>, whose existence in solution is dubious. Attempts to isolate it generally form Sb<sub>2</sub>O<sub>3</sub>÷xH<sub>2</sub>O, antimony(III) oxide hydrate, which slowly transforms into Sb<sub>2</sub>O<sub>3</sub>.
In geology, the mineral stibnite, Sb<sub>2</sub>S<sub>3</sub>, is sometimes called antimonite.
Antimonites can be compared to antimonates, which contain antimony in the +5 oxidation state.