Allophane–titania composite films were prepared from titanium alkoxide sols dispersing the natural clay mineral allophane as a nano-sized adsorbent. The composites of the titania dispersing the allophane particles in the whole film efficiently degraded trichloroethylene and acetaldehyde better than the normal titania and the titania dispersing the allophane only on the film surface. The titania dispersing the allophane particles in the whole film produced lower amounts of the intermediate products in certain stages than the titania. These results are due to the effective reactant transport from the allophane to titania. Photocatalytic degradation of glucose and photoelectrochemical measurements using an electrolyte solution containing glucose indicated that oxidative degradation of the glucose enhanced the generation of electricity during UV irradiation. A higher short circuit current was observed using the film dispersing the allophane on the surface layer with an ca. 50-nm thickness than the titania and those dispersing the allophane only on the film surface. Allophane effectively adsorbed the glucose molecules and transported them to the titania, then the products were desorbed into the liquid phase. Therefore, the holes were efficiently transported and consumed by the glucose oxidation.