The shear flow properties of aqueous silica suspensions at different Solids loading in the presence of polyethylene oxide (PEG) and added salt (NaNO3) have been investigated. Particular attention is given to the evaluation of the role of electrolyte concentration, pH, and polymer concentration in viscosity reduction. The variation of the rheological properties with shear rate, solids loading, particle size, pH, electrolyte concentration, PEO concentration, and its molecular weight are discussed. The viscosity of the silica suspension was determined to be a decreasing function of the particle diameter and at 54% volume, the effect of particle size was scaled using Peclet number and relative viscosity of the suspension (hard sphere scaling). The flow properties of silica suspensions are highly affected by the pH of the suspending media and concentration of the added salt. At a fixed electrolyte concentration, the viscosity decreases by increasing pH, reaches a minimum, and then increases with further increase in pH. At a fixed pH level, the same behavior was observed for viscosity as a function of electrolyte concentration. The effect of the electrolyte concentration is more significant at lower shear rates. It is shown that the rheological properties of silica suspensions are strongly affected by the concentration of the added polymer and its molecular weight. For each sample, there is a critical amount of polymer that must be added before low viscosities result. There is a nearly linear relation between the critical polymer concentration and volume fraction of the particles. The results of this work provide useful information for selection of a proper pH range, electrolyte concentration, and optimum polymer concentration to control the viscosity behavior of highly concentrated silica slurries.