Copper ion-modified titanium oxide and process for producing the same, and photocatalyst

The present invention relates to a copper ion-modified titanium oxide including titanium oxide whose surface is modified with a copper ion, and containing a brookite-type crystal; a process for producing a copper ion-modified titanium oxide, including a hydrolysis step of subjecting a titanium compound capable of producing titanium oxide to hydrolysis in a reaction solution, and a surface modification step of mixing a solution obtained after the hydrolysis with an aqueous solution containing a copper ion to modify a surface of the titanium oxide therewith; and a photocatalyst containing the copper ion-modified titanium oxide in an amount of 70% by mass or more.