Photosensitive ultrathin films with phosphate-containing polyanions and diazoresin (DR) as a polycation were fabricated with a self-assembly technique. The phosphate-containing polyanions were poly(sodium. phosphate), phosphorylated poly(vinyl alcohol), and DNA. The fabrication process was monitored by the determination of the absorbance from DR. The surface morphology of the multilayer films was observed with atomic force microscopy. Under ultraviolet irradiation, the linkage between the layers of the films changed from being ionic to being covalent; as a result, the stability of the films toward polar solvents increased. This kind of film may have applications for biosensor devices.