Red copper oxide or “copper oxide I” is an inorganic (mineral) chemical compound with chemical formula Cu₂O, which is used in agricultural industry as a fungicide and in the paint industry as a biocide in the paint of the ship hulls.

“Copper oxide I” is used in ceramic industry as a colorant and as a catalyst in some chemical processes. Recently, it is used in manufacture of solar cells due to the semiconducting properties of “copper oxide I”.