The antireflective (AR) properties of Al2O3 thin films with small roughness on soda-lime silica glass substrates were investigated. By immersing porous Al2O3 thin films in hot water, nanocrystals of pseudoboehmite were formed on the film surface. The reflectance of the Al2O3 films treated with hot water for 30 min was less than 0.5% in the wavelength region of 360-620 nm. The Al2O3 films with small roughness resulting from the hot water treatment become denser from their surface to the interface with the substrate, and the refractive index gradient brought by the structure results in excellent AR properties. (c) 2006 Elsevier B.V. All rights reserved.