Series of metal-doped TiO2 transparent aqueous sols were synthesized via a simple green chemical route. The as-synthesized samples were analyzed with HRTEM, XRD, EELS, and XPS, verifying that most metal ions have been doped with TiO2 forming Ti-O-Metal bond. These environmental-friendly doped TiO2 sols exhibited good photocatalytic activities under visible-light irradiation, and could be stably kept in sealed case for several months without precipitate, and it therefore may efficiently utilize solar energy or indoor light for industrial and household application without shape limitation. This method may be applied to synthesis of other metal-doped TiO2 sols. (C) 2012 Elsevier B.V. All rights reserved.