We report the size-selective photocatalytic decomposition of organic molecules using crystalline anodic TiO2 nanochannel films as the photocatalyst. The porous TiO2 films were formed by anodizing titanium at 20 V in glycerol electrolyte containing various amounts of K3PO4, K2HPO4, and KH2PO4 at 433K. Regardless of the electrolyte composition, the as-formed TiO2 films had a crystalline anatase structure. The basicity of the electrolyte markedly influenced the morphology of the TiO2 nanochannel films; more regular nanochannels developed with increasing basicity of the electrolyte. Because the diameter of the nanochannels in the films formed in a basic electrolyte was as small as similar to 10 nm, the anodic TiO2 nanochannel films with a thickness of 5 mu m revealed a selective photocatalytic decomposition of methylene blue (MB) in a mixture of MB and direct red 80 (DR) kept under UV irradiation. The importance of the diameter of the nanochannels and their uniformity for size-selective decomposition of organic molecules were investigated. (C) 2014 Elsevier B.V. All rights reserved.