Anodization of aluminum was examined in nonaqueous solutions containing a small amount of water, and the resul-tant anodic oxide films were characterized by SEM, TEM, AES, XPS, XANES, and FT-IR. The film properties were dependent on not only the kind of nonaqueous solutions but also the amount of water in the solutions. When the water content in nonaqueous solutions was decreased below 1∼0.1 %, anions and/or organic solvents were incorporated into the films and very different anodic films were formed. A phthalate/γ-butyrolactone solution gave a fibrous porous-type film accompanying solution decomposition, whereas in a maleate/γ-butyrolactone solution fast and efficient film formation was observed and a barrier-type film containing maleate anions as an oxygen source was obtained. A vanadate/ethylene glycol solution provided a very thick film due to the incorporation of the solvent rather than vanadate anions. The optimum content of water to give the composite oxide films seems to depend on the viscosity of the solutions.