Hysteresis in the electrokinetic behavior of colloidal hydrothermal BaTiO3 occurs during sequential acid and base titrations. Ba dissolution during acid titration results in an oxide-rich surface. When the acid-treated BaTiO3 is titrated back to pH 10, dissolved Ba is specifically adsorbed and/or precipitated onto the particle surface. The combined effects of dissolution and subsequent adsorption-precipitation results in titration hysteresis. Most of the labile Ba can be removed by multiple acid treatments, which result in a TiO2-Iike surface layer composition. Barium dissolution increases with decreasing pH but levels off below pH 4 due to diffusion through the surface oxide layer as predicted previously. A phenomenological model is offered to explain the electrokinetic behavior as a function of pH. It is suggested that inherent BaCO3 contamination is not the primary source of dissolved Ba from hydrothermal BaTiO3 in acidic solution.