Abstract: A hydroxyl group-containing (meth)acrylate oligomer represented by the general formula I: ##STR1## wherein two R.sup.1 's independently stand for hydrogen atom or methyl group, two Z's independently stand for a divalent organic group of 2 to 20 carbon atoms, and p stands for an integer of the value of 1 to 100, and urethane, carboxyl and hydroxyl modified prepolymer thereof.

Abstract: A composite semipermeable membrane comprising a porous support and a crosslinked thin film formed on said porous support, said crosslinked thin film being formed by reacting compound (A) which is at least one compound selected from the group consisting of polyalkylenimines and polyalkylenimine derivatives, compound (B) which is at least one compound selected from a group of compounds typified by piperazine, 2,5-dimethylpiperazine, 4-aminomethylpiperidine and 1,4,8,11-tetraazacyclotetradecane, and compound (C) as a crosslinking agent which is a compound having in one molecule two or more functional groups capable of reacting with amino groups; and a process for preparing said composite semipermeable membrane.