Iridium tetroxide (IrO4, Iridium(VIII) oxide) is a binary compound of oxygen and iridium in oxidation state +8.

[1] This compound was formed by photochemical rearrangement of [(η1-O2)IrO2] in solid argon at a temperature of 6 K (−267.15 °C; −448.87 °F).

At higher temperatures, the oxide is unstable.

[2] The detection of the iridium tetroxide cation IrO+4 by infrared photodissociation spectroscopy with formal oxidation state +9 has been reported, the highest currently known of any element.

[3][4] However no salts are known, as attempted production of an Ir(IX) salt such as IrO4SbF6 did not result in anything.