In order to produce highly concentrated bioethanol by pervaporation using an ethanolpermselective silicalite membrane, techniques to suppress adsorption of succinic acid, which is a chief by-product of ethanol fermentation and causes the deterioration in pervaporation performance, onto the silicalite crystals was investigated. The amount adsorbed increased as the pH of the aqueous succinic acid solution decreased. The pervaporation performance also decreased with decreasing pH when the ternary mixtures of ethanol/water/succinic acid were separated. Using silicalite membranes individually coated with two types of silicone rubber, pervaporation performance was significantly improved in the pH range of 5 to 7, when compared with that of non-coated silicalite membranes in ternary mixtures of ethanol/water/succinic acid. Moreover, when using a silicalite membrane double-coated with the two types of silicone rubber, pervaporation performance was stabilized at lower pH values. In the separation of bioethanol by pervaporation using the double-coated silicalite membrane, removal of accumulated substances having an ultraviolet absorption maximum at approximately 260nm from the fermentation broth proved to be vital for efficient pervaporation. (c) 2005 Society of Chemical Industry.