In this letter, copper nanoclusters formation was observed in Cu-doped silicate glasses after UV-light irradiation followed by thermal annealing. Spectroscopic data indicated that Cu(+) transferred to Cu atoms after irradiation. The aggregation of Cu atoms appeared after heating at 500 degrees C for 30 min, resulting in an absorption band at about 560 nm, due to the surface plasmon resonance of Cu nanoclusters in glass. The band intensity of the absorption peak increases with heating time at 500 degrees C. The mean nanocluster size estimated based on Mie theory was similar to 2.3 nm after heated at 500 degrees C for 120 min. The Cu nanoclusters only formed in the irradiated area of the glass. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.