The photoswitchable magnetic thin films have been designed by alternate depositions of bipolar amphiphilic azobenzene and Fe3O4 nanoparticles by using the layer-by-layer adsorption technique. In these films, reversible photoisomerizations of the azobenzene chromophore affected the electrostatic interaction between the azobenzene chromophore and the surface of Fe3O4 nanoparticles. As a result, we have succeeded in controlling the magnetization of these films by photoillumination at room temperature.