The rheological parameters of clay suspensions can be used to examine particle-particle interactions. The polymers that have been added to the clay suspensions interact with clay particles, according to their ionic or non-ionic character. In this study, the changes in the rheologic properties of three different samples, which are two different bentonitic clays and hectorite, have been studied with various concentrations of polyvinyl alcohol (PVA). It has been determined that the flow properties, such as apparent and plastic viscosity, shear stress and yield value point, change with the clay type, chemical properties of the additive material and their concentration. All the results have been commented by taking the interaction between the clay and the polymer molecules into consideration. XRD studied showed that natural bentonite samples have more expandable, up to 24 Angstrom, than other samples, which their expandibilities are relatively constant at about 15 Angstrom. (C) 2004 Elsevier B.V. All rights reserved.