Bentonite clay is the main component of the water- based drilling fluid. In this study the Egyptian bentonite from (south Hammam) was tested for its potential use in drilling fluids. The drilling mud quality of the bentonite from (south Hammam) was significantly improved by using low molecular weight polyvinyl alcohol (PVA) as a viscosifier additive. The Egyptian bentonite was characterized by X-ray fluorescence analysis (XRF), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and transition electron microscopy (TEM). The treated Egyptian bentonite was evaluated as drilling mud for oil–well drilling. The evaluation involves the study of the rheological properties (apparent viscosity, plastic viscosity, yield point, gel strength and thixotropy), filtration properties before and after treatment with polyvinyl alcohol as viscosifier additives. Effect of temperature on the formulated mud at different temperatures was also studied and the results were compared with the commercial grade bentonite according to American Petroleum Institute specification (API) and O.C.M.A specification.