Abstract: Water permeable reverse osmosis membranes are prepared by interfacially polymerizing on a microporous support an essentially monomeric polyamine reactant having at least two amine functional groups per reactant molecule, and an essentially monomeric amine-reactive polyfunctional single ring cycloaliphatic acyl halide having fewer than six carbon atoms per ring and having on the average at least about 2.2 acyl halide groups per reactant molecule. The polymerization is preferably carried out in the presence of a monomeric amine salt, which increases the flux rate of the resulting membrane. In addition, an aromatic polyfunctional acyl halide may be used in conjunction with the cycloaliphatic acyl halide in order to increase salt rejection rates. Preferred cycloaliphatic acyl halides are 1-cis, 2-trans, 3-cis, 4-trans-cyclopentane tetracarboxylic acid chloride, 1-cis, 2-trans, 3-cis, 4-trans-cyclobutane tetracarboxylic acid chloride and 1-cis, 2-trans, 4-cis-cyclopentane tricarboxylic acid chloride.