New 2-oxazoline group-containing copolymer crosslinkers for humidity-sensitive polyelectrolytes were prepared by copolymerization of [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (METAL), 2-isopropenyl-2-oxazoline (IPO) and n-butyl methacrylate (BMA). They were mutually crosslinkable with carboxylic acid-containing copolymers METAC/acrylic acid (AA)BMA = 10/2/8. When the polyelectrolytes were applied to the humidity-sensitive membranes, the resistance varied from 10(7) to 10(3) Omega between 20% RH and 95% RH, which was required for a humidity sensor operating at ambient humidity. Temperature dependence, hysteresis, response time, water durability and long-term stability at high humidity were also measured and estimated. (C) 2005 Elsevier B.V. All rights reserved.