Steady flow and dynamic viscoelastic properties of concentrated aqueous disperse systems of colloidal silica spheres (diameter 8, 15, and 45 nm) have been measured in the deionized (salt‐free) state and in the presence of added salt NaCl. In the deionized state, the disperse system of the particle of 45 nm diameter shows high viscosity and typical so‐called yield stress, however, it shows Newtonian flow at extremely low shear rate. On the other hand, the system shows low viscosity and Newtonian flow in the ionized state. The transition from high viscosity to low viscosity state is very sharp. The deionized system shows nonlinear dynamic viscoelasticity even at strains as small as0.1∼0.2%.The disperse systems of smaller particle show Newtonian flow, irrespectively, at the deionized and the ionized states. The change in viscosity between the two states is very small. These results can be explained by the order‐disorder transition of colloidal systems, the effect of the particle size, and the Debye screening length.