Chitosan is an aminopolysaccharide produced from crustacean shells. This biopolymer is very efficient at sorbing metal ions through different mechanisms including (a) chelation on its amine group in near-neutral solutions or (b) ion exchange in acidic solutions (protonated amine groups interact with metal anions). Alternatively, dissolved chitosan can be used for the recovery of metal ions using Polymer-Enhanced Ultrafiltration (PEUF) technique. The process makes profit of the ability of the macromolecules to bind metal ions and to be retained by membranes of selected cut-off. The process has been tested in the case of mercury using an Amicon ultrafiltration system. The efficiency of the process has been investigated using membranes of different cut-off (10 kDa, 50 kDa, 100 kDa). The influence of pH, metal concentration, chitosan concentration and pressure has been studied on permeation flux and the retention of both the polymer and the metal. The coupling of metal binding and ultrafiltration allows reaching retention efficiency greater than 95% under appropriate experimental conditions. For mercury, metal recovery occurs by chelation and the optimum pH is close to pH 5-6. The mercury/chitosan binding constant has been determined close to 107.3