Abstract: Disclosed is a composite thin film that can be expanded in surface area of an organic compound film having a surface, on which specific molecules are adsorbed, can increase the number of reactive sites per single layer of the organic compound film, and can be produced with a low number of laminations, and is excellent in productivity. The composite thin film is furthermore excellent in applicability in enabling reactive sites to be modified with a functional molecule to enable application to sensors of high sensitivity and molecular devices, etc., of improved function. The composite thin film is formed on a surface of a support and is characterized in that the composite thin film has at least one layer of each of the following films of (a) and (b) on the surface of the support. That is, (a) a microparticle film formed by adsorption of microparticles, and (b) an organic compound film formed by adsorption of an organic compound.