A titration procedure was used to determine the zero point of charge of a number of chloride-containing aluminum hydroxide gels and aluminum hydroxycarbonate gels. The surface charge characteristics of aluminum hydroxide gel were determined by both hydroxyls and the surface density of specifically adsorbed carbonate anion. The wide range of zero point of charge values reported for aluminum hydroxide is thought to be due to the presence of specifically adsorbed anions such as carbonate. The effect of ionic strength on the pH of aluminum hydroxide gel is important during washing since the ease of electrolyte removal is related to surface charge. Viscosity and sedimentation characteristics are related to the relationship between the zero point of charge and bulk pH. Maximum possibility was observed when the bulk pH was adjusted to the zero point of charge.