Due to their exceptional rheological properties, bentonites are used in different branches of industry, such as in drilling fluids, dyes, pharmaceuticals, paper, cement, nanocomposites, polymer composites, and ceramics. In the use of bentonite in different applications, the addition of carboxymethyl cellulose (CMC) sodium salt is recommended to optimize the rheological properties of the suspension. In this study, the effect of carboxymethyl cellulose on the rheological properties of Na-bentonite suspensions was investigated in the polymer concentration range of 0.02-0.50 wt%. The addition of carboxymethyl cellulose to the bentonite dispersions resulted in significant increase in the dispersion viscosity. The advantage of carboxymethyl cellulose is that the desired rheological properties can be obtained with less bentonite by adding carboxymethyl cellulose polymer and the undesirable effects of high bentonite concentrations can be avoided. The viscosity of 8.0 wt% pure bentonite dispersions was achieved by adding 0.10 wt% carboxymethyl cellulose to 4.0 wt% bentonite dispersions. The combined flow behaviors of Bingham and shear thickening observed for the 4.0 wt% pure bentonite dispersion was shifted toward the shear thinning profile with a yield stress in the presence of the carboxymethyl cellulose. This yield stress increased substantially with carboxymethyl cellulose concentration. In addition, the thixotropic behavior of bentonite dispersions was significantly enhanced by adding carboxymethyl cellulose polymer.