Lead magnesium niobate (PMN) is an important relaxor ferroelectric material commonly used in multilayer capacitor and actuator manufacturing owing to its high dielectric constant and superior electrostrictive properties. However, the isoelectric point of this material in water is not known and there is justification for a detailed investigation. In this work, the isoelectric point (IEP) of aqueous PMN suspensions were determined as a function of solids concentration. Results showed that IEP of the PMN suspensions strongly depended on the solids loading. The IEP was between pH 9 and 10 at particle concentrations between 10 to 20 vol%. The IEP shifted gradually to a lower pH value as the particle concentration decreased. Solubility experiments showed that Pb2+ and Mg2+ ions dissolved from the PMN surface, especially in the acidic pH range. The study provides a new insight on the aqueous stability of perovskite materials which possess more than one soluble cation in their structure.