PROBLEM TO BE SOLVED: To provide a composite film exhibiting photochromism, which is excellent in film forming property and transparency in a dark environment, shows high light-shielding property by irradiation with light, and can be used as a dimming film or the like.SOLUTION: The composite film comprises a transition metal oxide, a water-soluble polymeric compound, and a water-soluble compound having a hydroxy group (excluding the above water-soluble polymeric compound). The transition metal oxide is preferably tungsten oxide. The water-soluble polymeric compound is preferably an alkyl cellulose such as methyl cellulose. The water-soluble compound having a hydroxy group is preferably alcohols such as ethylene glycol and glycerol or organic acids such as oxalic acid and glycolic acid. As the composite film develops a color by irradiation with UV rays, the film is useful as a dimming film, a recording medium, a photoreceptor for blueprint (cyanotype), or the like.
