In this paper, a new method is introduced to produce sodium bentonite by treating calcium bentonite using seawater to eliminate the use of freshwater and reduces the amount of soda ash required for the treatment, which significantly minimizes the cost of bentonite production. In this study, calcium bentonite was collected as rocks from local resources, ground, purified, characterized, and the physical properties were measured. Then, bentonite was treated using seawater under heating and stirring for different time periods to optimize the treatment conditions. Soda ash was also added with different concentrations, and the produced bentonite samples were characterized, evaluated, and compared to the standard sodium bentonite used in drilling fluid formulation. The results of this study showed that the treatment with soda ash under heating and stirring in seawater environment converts calcium bentonite into sodium bentonite by sodium and calcium cations exchange between soda ash and calcium bentonite. This exchange will improve the rheological and swelling properties of bentonite that can efficiently be used as a drilling fluid and cement additive.