Two kinds of urease-immobilized polymer membranes were prepared. One was prepared by bulk-copolymerizing a mixture consisting of vinylized urease (VU), acrylamide (AAm), 2-hydroxylethylmethacrylate (HEMA) and a cross-linker (urease-immobilized poly(VU-AAm-HEMA) membrane) and another was prepared by ultrafiltrating a mixture composed of urease, quaternized chitosan and sodium carboxymethylcellulose in an aqueous sodium bromide solution (urease-immobilized polyion complex membrane). The permeation and hydrolytic characteristics of aqueous urea solutions were kinetically investigated under various conditions through urease-immobilized membranes. The hydrolysis of urea through urease-immobilized membranes followed Michaelis-Menten kinetics and is discussed herein. (c) 2006 Elsevier B.V. All rights reserved.