The point of zero charge (pH(pzc)) of three samples of commercial aluminum oxide in aqueous KNO3 (10(-3) - 10(-1) mol/dm(3)) solution was investigated using batch equilibration, mass titration and acid-base titration methods. Structural and chemical characteristics of the alumina samples were determined by X-ray diffraction (XRD) and energy-dispersive X-ray fluorescence spectroscopy (EDXRFS). The obtained pH(pzc) values (5 to 8.5) dependent on the alumina/solution ratio increase with increasing ratio to a constant value. The concentration of dissolved aluminum ions as a function of solution pH (pH = 3.5 - 11) exhibit a parabolic trend, with the minimum solubility at pHpzc.