A stable colloidal suspension is important for fabricating dense samples with uniform microstructure using colloidal processing methods. Aqueous nano-Zr02 suspensions were prepared using polyethylenimine (PEI) as a dispersant. The isoelectric point (IEP) shifts from pH 7 at 0 wt% PEI to pH 10.3 at 3 wt% PEI. Stable suspensions had mean particle sizes in the range of 100 to 150 nm and sedimentation rates less than 0.4 mm/h, as compared to 2-5.5 |im and 10-50 mm/h for unstable suspensions. Electrostatic interactions, hydrogen bonding and PEI conformation were found to be controlling mechanisms on the colloidal stability of the suspensions. The amount of PEI adsorbed on nano-Zr0₂ surfaces was characterized using Thermogravimetric analysis (TG) and Fourier transform infrared spectrometer (FT-IR). The densification behavior of samples containing 3 wt% PEI at pH 7.1 sintered for 4 h at 1000 to 1300 °C was characterized.