Silica nanoparticles and thin film on flat substrate were simultaneously prepared by the Stober method. The growth kinetics of these precipitates and the fine structure of the film surface were investigated by atomic force microscopy. The thin film formed on a hydrophilic substrate was flat and uniform, with root-mean-square (RMS) roughness of approximate to 1 nm. The growth of the film was observed to be slower than that of the particles, indicating that the growth of these silica precipitates was limited by the diffusion of reactive silica species. On the other hand, the thin film formed on a hydrophobic substrate was not flat, with RMS roughness of approximate to 10 nm, and was characterized by convex microstructures of two distinct sizes on its surface. The appearance of these microstructures and the delay observed in film formation on the hydrophobic surface indicate that these precipitates, including spherical Stober colloids, formed as aggregations of primary particles appearing in the precursor solution, and then grew by the adhesion of primary particles forming continuously in the solution. (C) 2003 Elsevier Science B.V. All rights reserved.