In this study, the rheological properties of Na-bentonite (NaB), sepiolite (Sp) and the mixture of 2% NaB and 1% Sp from Enez and Eskisehir clay deposits of Turkey were investigated. According to flow properties of the mixture, it was observed that the mixture is not adequate to be a suitable drilling fluid. The main idea was to make stable dispersions with bentonite and sepiolite by using a water soluble polymer as a stabilizer. The changes in the rheological properties of bentonite and sepiolite were studied with various concentrations of polyvinyl alcohol (PVA) to find out the stability of the dispersions. The concentrations, which showed stability for NaB and Sp, were used to stabilize and to change the flow properties of the NaB-Sp dispersion. To determine the interactions, the clay content of the mixture was kept less than the drilling fluid standards of API. The rheological properties of the dispersions were determined at different temperatures. Using the results, the drilling fluid was prepared according to API standards. Moreover, the standard API tests were applied to the drilling fluid to determine the properties of dispersions. (C) 2010 Elsevier B.V. All rights reserved.