Xenon tetroxide is a chemical compound of xenon and oxygen with molecular formula XeO₄, remarkable for being a relatively stable compound of a noble gas. It is a yellow crystalline solid that is stable below −35.9 °C; above that temperature it is very prone to exploding and decomposing into elemental xenon and oxygen (O₂).

All eight valence electrons of xenon are involved in the bonds with the oxygen, and the oxidation state of the xenon atom is +8. Oxygen is the only element that can bring xenon up to its highest oxidation state; even fluorine can only give XeF₆ (+6), though attempts to synthesize XeF₈ (+8) are still being made.

Two other short-lived xenon compounds with an oxidation state of +8, XeO₃F₂ and XeO₂F₄, are accessible by the reaction of xenon tetroxide with xenon hexafluoride. XeO₃F₂ and XeO₂F₄ can be detected with mass spectrometry. The perxenates are also compounds where xenon has the +8 oxidation state.

At temperatures above −35.9 °C (−32.6 °F), xenon tetroxide is very prone to explosion, decomposing into xenon and oxygen gases with ΔH = −643 kJ/mol:

Xenon tetroxide dissolves in water to form perxenic acid and in alkalis to form perxenate salts:

Xenon tetroxide can also react with xenon hexafluoride to give xenon oxyfluorides:

All syntheses start from the perxenates, which are accessible from the xenates through two methods. One is the disproportionation of xenates to perxenates and xenon:

The other is oxidation of the xenates with ozone in basic solution: