We report on precipitation of Ag nanoparticles in silicate glasses by a femtosecond laser irradiation and successive annealing. Effect of Al2O3 on the precipitation of Ag nanoparticles in glasses was investigated. Absorption spectra show that introducing a small amount of Al2O3 results in inhibition of color centers generation and an apparent increase of the annealing temperature for the precipitation of Ag nanoparticles. The mechanisms of the observed phenomena are discussed. (C) 2003 Elsevier B.V. All rights reserved.