The aqueous dispersions of C. I. Disperse Blue 79 of different concentrations were prepared in the presence of anionic or nonionic surfactants in this research. The influences of simple inorganic electrolyte on the stability and the electrokinetic properties of the dispersions were studied by using the settlement value as the stability parameter

and the electrokinetic potential as the parameter of the electric double layer of the particles. Good agreement was obtained between the two parameters. The results showed that the simple inorganic electrolyte might initially increase the stabilities of the dispersions at low concentration by assisting the building-up of the electric double layer

but decrease the stabilties by compressing this double layer when its concentration went beyond a critical value. Although the increase of the adsorption of surfactants on the dye particles caused by the increasing concentration of the electrolyte might increase the absolute value of the electrokinetic potential and there are increase the stabilities of the dispersions

the direct influence of the electrolyte on the electrie double layer was always dominant.