This work focuses on the effect of poly(dimethyl siloxane) (PDMS) cross-linking on the permeation performance of the poly (acrylonitrile) (PAN)/PDMS nanofiltration (NF) composite membrane. PDMS membrane of various cross-linking degrees could be obtained by changing the ratio of a vinyl-terminated pre-polymer over a hydride cross-linker, 10/0.7, 10/1 and 10/2. The hexane permeability (P-hexane) through the PAN/PDMS composite membrane prepared at pre-polymer/cross-linker ratio of 10/0.7 is higher than at ratio of 10/1 (4.5 and 3.1 lm(-2) h(-1) bar(-1), respectively), due to the higher membrane swelling. The P-hexane through the PAN/PDMS prepared at pre-polymer/cross-linker ratio of 10/2 is however higher than through the composite membrane prepared at 10/1 ratio (4.1 and 3.1 lm(-2) h(-1) bar(-1)). This result is not consistent with the swelling findings of the dense, free-standing PDMS membranes and might be due to the lower pore intrusion of the composite membrane prepared at ratios of 10/2 compared to 10/1 and/or due to the heterogeneous quality of the silicone network. The "apparent" viscosity inside the membrane and the membrane swelling are the most critical factors affecting the hexane permeability through all composites. Nevertheless, the composite membranes prepared at various pre-polymer/cross-linker ratios have similar oil and/or PIB retention probably due to the high swelling of the silicone network. (C) 2005 Elsevier B.V. All rights reserved.