Dichlorine trioxide, Cl2O3, is a chlorine oxide.

It is a dark brown solid discovered in 1967 which is explosive even below 0 °C.

Its structure is believed to be OCl−ClO2 with possible isomers such as Cl−O−ClO2.

[3] The isomer having a structure of OCl–O–ClO would be the theoretical anhydride of chlorous acid.

This inorganic compound–related article is a stub.