The surface of ${gamma}$-alumina, which has limited uses due to its low surface activity, was treated with nitric acid, and the effects of surface activity on the surface electrical characteristics were investigated. The ${gamma}$-alumina was prepared by the precipitation of aluminium nitrate [Al(NO3)3.9H2O] usign ammonia water as a precipitator. After chemical treatment with acid, the interfacial electrical phenomena and the acid-base characteristics were experimentally determined. The acidity of a ${gamma}$-alumina is linearly dependent on the point of zero charge when the ${gamma}$-alumina was dispersed in aqueous electrolyte solution. The surface and the morphological properties of the acid-treated ${gamma}$-alumina were analysed by BET and FT-IR, and the surface activities were measured by the Hammet indicator and amine titration methods. The interfacial properties of the ${gamma}$-alumina dispersed in electrolyte solution were estimated by the surface charge density which was measured by the potentiometric titration method. Based on the relation between surface charge density which was measured by the potentiometric titration method. Based on the relation between surface charge density and the acid amount, the following results were drawn for the surface characteristics and interfacial electrical properties; The acidity of surfacetreated alumina is linearly dependent on the point of zero charge when the ${gamma}$-alumina was dispersed in aqueous electrolyte solution. The acidic properties increase and the surface ionization constants decrease with increasing anion load on alumina surface. Acid amount of surface treated alumina can be correlated with surface charge density at the condition of H0 ＋4.8 as follows; QA=-0.024$sigma$-0.0189