The colloidal stability of aqueous Al2O3/ZrO2 and Al2O3/SiC suspensions in the presence of electrolyte was investigated by rheological measurement. It was observed that the stability of binary systems improved with increasing ionic strength, where the solution pH value was maintained in the middle range of the two isoelectric points of the constituent powders. In this case, the electrostatic attractive interaction between dissimilar particles became more prominent when their number ratio approached unity. In addition, the salt-dependent stability was studied over the entire range of pH and relative component fraction. The results showed that the role of ionic strength in promoting flocculation or stabilization of colloidal dispersions was mainly determined by the predominant electrostatic interaction between particles, and the experimental stability maps were used to distinguish the stable and unstable suspensions with the addition of an electrolyte.