Protactinium(IV) oxide is a chemical compound with the formula PaO<sub>2</sub>. The black oxide is formed by reducing Pa<sub>2</sub>O<sub>5</sub> with hydrogen at 1 550 ðC. Protactinium(IV) oxide does not dissolve in H<sub>2</sub>SO<sub>4</sub>, HNO<sub>3</sub>, or HCl solutions, but reacts with HF.
As protactinium(IV) oxide, like other protactinium compounds, is radioactive, toxic and very rare, it has no known technological use.