Polyethylenimine (PEI, M(w) 50,000) was employed as a dispersant to stabilize nanosized ZrO(2) (3 mol% Y(2)O(3) doped) aqueous suspensions. Adsorption isotherm measurements demonstrated that the plateau region of coverage was reached when polymer concentration approached 1.0 wt% dry weight basis of ZrO(2) and beyond at fixed pH values. The positively charged polymer chains showed a high affinity type of adsorption on nanosized ZrO(2) particles. Obviously, the amount of dispersant adsorbed on ZrO(2) particles at pH higher than the isoelectric point was greater than the amount adsorbed at low pH. FTIR spectral analysis of the polymer-anchored ZrO(2) nanoparticles strongly supported the conclusion that the adsorption was accompanied by the formation of a ZrO(2)/PEI interface complex. The mechanisms of PEI adsorption on ZrO(2) nanoparticles were dominated by hydrogen bonding and electrostatic attraction. Copyright 1999 Academic Press.