The properties of the liposome membrane as a reaction field were investigated by focusing on the Horner-Wadsworth-Emmons reaction as a case study. Use of the liposomes existing in the gel phase resulted in the enhanced activity of the substrates and furnished the products with same E/Z stereoselectivity as in the liposome-free system. The membrane environment in the gel phase most likely assisted the formation of adducts that induced selective generation of the E-isomer. The possible role of liposomes is to assist the proton removal from the reactant, rather than providing the basic interfacial environment. (C) 2019, The Society for Biotechnology, Japan. All rights reserved.