Properties of α-alumina surface, dissociated fraction of polyacrylic acid, and the interaction between alumina surface and polyacrylic acid were investigated in aqueous suspensions in the pH range of 2.2 to 10.5. The isoelectric point of the colloidal α-alumina particles was pH 7.7, and the surface was charged positively and negatively at pH below and above 7.7, respectively. The dissociated fraction of polyacrylic acid changed with pH, close to 0% at pH below 3 and 100% at pH above 9. Polyacrylic acid was adsorbed on the alumina particles as neutral polymer at low pH and negatively charged polymer at high pH. The total amout of adsorbed polymer decreased with an increase in pH due to the repulsive interaction between the negative particle surface and negatively charged polymer.