A method of preparing a solution for titanium oxide film is provided such that said solution has the effect of a photocatalyst, by coating, or impregnating therewith a variety of substrates being positioned in a place where no ultraviolet light is emitted. Utilizing a solution for titania film provided by a mixture of a titanium peroxide solution made from a compound of a titanium hydrate gel and a peroxide solution, and a solution forming titanium peroxide particles by calcining said titanium peroxide solution at a temperature over 80.degree. C., particles of capsicin, magnetite and tourmaline, as well as a silica solution are each compounded to said solution for titania film, such that an improved solution for titania film can be obtained having the photocatalystic effect without any exterior light source.