Vanadium(II) oxide is the inorganic compound with the idealized formula VO. It is one of the several binary vanadium oxides. It adopts a distorted NaCl structure and contains weak V−V metal-to-metal bonds. VO is a semiconductor owing to delocalisation of electrons in the t<sub>2g</sub> orbitals. VO is a non-stoichiometric compound, its composition varying from VO<sub>0.8</sub> to VO<sub>1.3</sub>.
Diatomic VO is one of the molecules found in the spectrum of relatively cool M-type stars. A potential use of vanadium(II) monoxide is as a molecular vapor in synthetic chemical reagents in low-temperature matrices.