Chitosan polymer was added to the montmorillonite (MMT) dispersions in different concentrations in the range of 1 x 10(-2)-50 x 10(-2) g/L (in 1% acetic acid solution). The rheological behaviours and colloidal properties of the clay dispersions were determined as a function of increasing polymer concentration. The studies on zeta potential measurements indicated that chitosan attached on the surface of clay particles. XRD analyses displayed that organic molecules did not enter enough sufficiently into the layers of clay structures. In the second part of the study, the rheological behaviour of 1 g/L chitosan dispersion in 1% acetic acid solution was investigated. Flow curves were analyzed using the Bingham model. The MMT/chitosan dispersions prepared at concentrations in a range of 1-50 g/g, and then rheological and electrokinetic measurements were repeated for these samples and studied together with the first measurements. The characterization with different methods (FTIR, AFM, DSC, and TGA) on chitosan-MMT biocomposite systems was examined. (c) 2006 Elsevier Ltd. All rights reserved.