Various branched polymers with different functionalities and side chains were synthesized as dispersant and their molecular structures were characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance, and thermogravimetric analysis (TGA) methods. It was found that the amount of side chain and kind of acidic or ionic functions had influences on the properties of the dispersants. The effect of side chain density of the dispersants on the intercalation of sodium montmorillonite (Na-MMT) was also investigated. The results of X-ray diffraction, and FTIR and TGA analyses showed that the branched polymers with a higher amount of side chains and acidic functions were suitable to provide efficient intercalation and adsorption. In addition, a weak intercalation of dispersant with a lower side chain density and neutral functions into the Na-MMT interlayer was observed. The role of side chain density and acidic/neutralize functionalities of dispersants on both the yield stress and viscosity of reactive silica fume suspensions was investigated. It was found that the dispersant with acidic functionalities and low amount of side chains increased the yield stress and viscosity. A lower viscosity was also recorded for the suspensions in the presence of Na-MMT. Moreover, the suspension prepared by the dispersant with a high side chain density exhibited higher fluidity and lower viscosity.