The present disclosure provides a composite optical film including a brightness enhancement film, a high refractive-index layer, and an intermediate layer. The brightness enhancement film has a plurality of brightness enhancement structures parallel to each other, and a top surface and a bottom surface opposite to each other. The brightness structures are disposed on the top surface. The high refractive-index layer is disposed on the bottom surface, and includes a film and a plurality of inorganic nano-particles disposed within the film. The intermediate layer is disposed between the brightness enhancement film and the high refractive-index layer.