Disclosed is a modified photocatalyst sol comprising a liquid medium having dispersed therein particles of a modified photocatalyst, wherein the modified photocatalyst particles are prepared by subjecting particles of a photocatalyst to a modification treatment with at least one modifier compound selected from the group consisting of different compounds each of which independently comprises at least one structural unit selected from the group consisting of a monooxydiorganosilane unit, a dioxyorganosilane unit and a difluoromethylene unit, and wherein the modified photocatalyst particles have a specific volume mean particle diameter. Also disclosed is a modified photocatalyst composition comprising the modified photocatalyst sol and a functional substance. Also disclosed are a film formed using the above-mentioned modified photocatalyst sol or modified photocatalyst composition, a functional composite comprising the film and a substrate covered with the film, and a shaped article produced by shaping the above-mentioned modified photocatalyst composition.