Provided are a functional composite film having one or more combinations of an inorganic layer and an underlying organic layer on one surface thereof, and having a light diffusion layer on the opposite surface, in which the light diffusion layer is formed by dispersing a light diffusing agent in a binder formed using a graft copolymer having a molecular weight of 10,000 to 3,000,000 and an acryl equivalent of 500 g/mol or more, which has an acrylic polymer as the main chain and at least one of a urethane polymer with an acryloyl group at a terminal or a urethane oligomer with an acryloyl group at a terminal in the side chain; and a wavelength conversion film using the same. Using these, a functional composite film and a wavelength conversion film, having good light diffusion performance and light transmittance are provided.