Diphosphorus tetroxide, or phosphorus tetroxide is an inorganic compound of phosphorus and oxygen.

It has the empirical chemical formula P2O4.

Solid phosphorus tetroxide (also referred to as phosphorus(III,V)-oxide) consists of variable mixtures of the mixed-valence oxides P4O7, P4O8 and P4O9.

[1][2][3] Phosphorus tetroxide can be produced by thermal decomposition of phosphorus trioxide, which disproportionates above 210 °C to form phosphorus tetroxide, with elemental phosphorus as a byproduct: In addition, phosphorus trioxide can be converted into phosphorus tetroxide by controlled oxidation with oxygen in carbon tetrachloride solution.

[4][5][6] Careful reduction of phosphorus pentoxide with red phosphorus at 450-525 °C also produces phosphorus tetroxide.