Polydimethylsiloxane (PDMS) hollow-fiber membranes grafted with 1H,1H,9H-hexadecafluorononyl methacrylate (HDFNMA), which is a fluoroalkyl methacrylate, using a Co-60 irradiation source, were characterized and applied to pervaporation. The PDMS hollow-fiber membranes were filled with NZ gas and sealed. The membranes and the HDFNMA solution were then irradiated simultaneously. In the HDFNMA solution, graft polymerization was performed. The degree of grafting of the outside surface of the hollow fiber was greater than that in the inside surface of the hollow fiber. In the grafted PDMS hollow-fiber membranes, the best separation performance was shown due to the introduced hydrophobic polymer, poly(HDFNMA). The grafted membrane had a microphase-separated structure, that is, a separated structure of PDMS and graft-polymerized HDFNMA. The permeability of molecules in the poly(HDFNMA) phase was so low that the diffusion of molecules was prevented in the active layer with many poly(HDFNMA) domains, as the feed solution was introduced through the inside of the hollow fibers and the outside was vacuumed. As the feed solution was introduced through the outside of the hollow fibers and the inside was vacuumed, the diffusion of molecules was not prevented in the active layer with few poly(HDFNMA) domains. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1573-1580, 2003.