Nanoporous titania membranes, with pore sizes ranging from I to several nm, were prepared by sol-gel processing and applied to permeation of hexane as a model nonaqueous solution system. TiO2 membranes showed a deceased hexane flux with an increase in water concentration, which was dissolved in hexane from zero to several hundred ppm. Nanopermporometry characterization before and after hexane permeation showed no change in pore structures of TiO2 membranes. Therefore, it was suggested that the dissolved water adsorbed to the hydrophilic TiO2 surface and reduced the effective pore size for hexane permeation. Negative rejection was observed in nanofiltration of linoleic acid in hexane solutions, that is, the linoleic acid was concentrated in permeate. Negative rejection was enhanced with decreasing pore diameter.