The objective of this work is to provide some elements for developing a theoretical methodology aimed to describe the ion conductivity mechanism of chitosan membrane and to obtain its magnitude. Atormstic molecular modeling has been utilized to construct an ionic-conducting polymer-electrolyte system consisting of chitosan, H2O molecules and H3O+, OH-, SO42- ions, inside of the simulation cell. The COMPASS force field was used. The simulation allows describing the ionic conductivity mechanism along the polymer matrix. The theoretical results obtained are compared with previously reported experimental data for chitosan membranes. The present methodology can be considered as a first step towards understanding these complex problems of technological interest. (c) 2005 Elsevier Ltd. All rights reserved.