Morphological properties of hydrophilic and hydrophobic Shirasu-porous-glass (SPG) membranes were investigated over a wide range of mean pore sizes (0.252-20.3 mu m) by liquid permeability measurements, scanning electron microscopy and Hg porosimetry. Hydrophobic modification of membrane surface was made by surface coating with silicone resin. The results are discussed using the non-uniform capillary bundle model of membrane permeability. The mean pore tortuosity of 1.28 was kept constant over the whole range of mean pore sizes investigated. The SEM images confirmed that the geometry of pore network was similar for all SPG membranes, irrespective of their mean pore size. The span of pore size distribution ranged from 0.28 to 0.68 and the number of pores per unit cross-sectional membrane area from 10(9) to 10(11) m(-2). The membrane resistance was unchanged after surface treatment with silicone resin, which means that the pores were not plugged by the resin, even in the submicron range of mean pore sizes. (c) 2004 Elsevier B.V. All rights reserved.