The objective of this research is to investigate the rheological and thermal properties of bentonites for water base drilling fluids. Rheological experiments were performed with 4 different bentonite samples and clay percentages, cation-exchange capacity (CEC), swelling volume, pH, and physical and rheological properties of the samples are determined. The thermal behaviors of bentonite samples were investigated using simultaneous thermogravimetry (TG/DTG) and differential thermal analysis (DTA) techniques. It was observed that all bentonite samples exhibit 2 weight loss events on heating. Similar behavior was observed with the bentonite samples studied in the literature.