Polonium monoxide (also known as polonium(II) oxide) is a chemical compound with the formula PoO.

It is one of three oxides of polonium, the other two being polonium dioxide (PoO2) and polonium trioxide (PoO3).

Polonium monoxide is a black solid.

It is formed during the radiolysis of polonium sulfite (PoSO3) and polonium selenite (PoSeO3).

[1][2] On contact with oxygen or water, both polonium monoxide and its related hydroxide (polonium(II) hydroxide, Po(OH)2) are oxidized quickly to Po(IV).