Polymethylmethacrylate (PMMA) films containing HAuCl4 (number density of 6 x 10(19) cm(-3)) were irradiated by a UV lamp and then annealed at various temperatures. The modification of the samples was investigated by in situ optical absorption spectroscopy and atomic-force microscopy (AFM). The disappearance of HAuCl4 followed by gold nanoparticles growth in the films was revealed. The evolution of the size distribution of the nanoparticles during annealing was investigated using the Mie theory. The growth kinetics model based on the non-stationary first-order phase transition theory estimates a critical radius of 2 nm for the growing nanoparticles at 75 degrees C. (c) 2005 Elsevier B.V. All rights reserved.