Crystalline ZnO nanoparticles were synthesized via the templating method by taking advantage of the hydrophilic cavities of the Nafion ionomer membranes. The ZnO-embedded Nation film was characterized by various methods, including optical absorption, X-ray diffraction and high-resolution transmission electron microscopy. The film was of high optical quality, and exhibited excellent photocatalytic activity toward rhodamine B degradation under UV irradiation. Unlike unprotected bulk ZnO nanocrystals, the ZnO nanocatalysts embedded in Nafion membranes were found to be highly stable against photocorrosion, with hardly any reduction in the activity even after 10 times of repeated reaction cycles. The implications of the results are discussed. (C) 2007 Elsevier B.V. All rights reserved.