The electrochemical behaviour of aqueous suspensions of ZrO2 powders, either pure phase (monoclinic and tetragonal) or mixtures of polymorphs, was investigated. Surface charge and total capacitance vs. pH curves, for the pure oxides, were regular showing different values of points of zero charge and low inner layer capacitance values. The mixtures of the polymorphs presented atypical interfacial electrochemical features which were interpreted as due to patch wise heterogeneity. This latter hypothesis was supported by XPS analyses of the powders which indicated, in the case of the mixtures of the polymorphs, the presence of heterogeneity both in composition and in the acid-base character of the surface sites.