Actinium(III) oxide, with the chemical formula Ac2O3, is a chemical compound composed of actinium and oxygen. In this compound, actinium is in the +3 oxidation state, having lost three electrons, and oxygen is in the -2 oxidation state, having gained two electrons.

As with other actinium compounds, actinium(III) oxide is a rare and radioactive substance. Actinium is a silvery-white, soft, and highly radioactive metal that is found in trace amounts in uranium and thorium ores. Due to its scarcity and radioactivity, actinium and its compounds have limited practical applications.

Actinium(III) oxide is primarily of interest in scientific research and studies related to actinium chemistry and properties. Because of the radioactive nature of actinium, proper safety precautions and handling procedures are essential when working with actinium(III) oxide or any other actinium compounds.

Overall, actinium(III) oxide is not a commercially significant compound, but it remains an essential material for researchers studying the behavior of actinium and its compounds in various chemical and physical processes.