Positron annihilation lifetime, spectra were measured for mesoporous silica films, which were synthesized using triblock copolymer (EO106PO70EO106) a; a structure-directing agent. Different positron lifetime spectra for the deposited and calcined films indicated the formation of meso-structure after calcination, which was confirmed by Fourier transform infrared (FTIR) spectra and field emission-scanning electron microscopy (FE-SEM) observation. Open porosity or pore interconnectivity of a silica film might be evaluated by a two-dimensional positron annihilation lifetime spectrum of an uncapped film. Pore sizes and their distributions in the silica films were found to be affected by thermal treatments. (c) 2005 Elsevier B.V All rights reserved.