The influence of the non-ionic (PEG) and cationic (modified polyethylene glycol, OEG-QDMA) polymers on the rheological and colloidal properties of Na-montmorillonite dispersions was investigated. The zeta potential and viscosity measurements were carried out as a function of polymer type (non-ionic and cationic) and their concentrations (0,01-100 g/L). The experimental data were interpreted taking into account these two parameters. 2 -(dimethylamino)ethyl methacrylate (DMA) was polymerized with monomethoxy-capped oligo(ethylene glycol), OEG, by using aqueous atom transfer radical polymerization (ATRP) chemistry. The tertiary amine residues of the resulting polymer were then quaternized with methyliodide in order to obtain cationic polyelectrolyte. The rheological parameters (the plastic viscosity and the yield value) were obtained by shear stress-shear rate measurements in a rotational low-shear rheometer. The zeta potential of the Na-montmorillonite particles was measured as a function of polymer concentration. The results indicated that non-ionic PEG adsorbed on the clay surface through hydrogen bonding. The plastic viscosity increased with an increase in the molecular weight of PEG. We observed a gradual increase in gelation by the addition of the cationic polymer which reached a maximum at the cationic polymer concentration between 0.4-0.8 g/L. Further increase in the cationic polymer concentration results with a reduction in this gelation.