Crack-free ultrafiltration zirconia membranes were synthesized using zirconium butoxide via the sol-gel route. Unlike the conventional technique, the esterification of anhydrous butanol and glacial acetic acid provided the hydrolyzing water. In addition, acetic acid also served as a chelating ligand to stabilize the hydrolysis-condensation process and minimize the agglomeration of zirconia. Esterification was verified by its product, butyl acetate, as identified by a GC/Mass. FTIR spectrum confirmed the presence of bidental ligand. HNO3 was used to perform the peptization, creating a stable particulate sol with pH near 1. The sol was spin-coated on anodic alumina discs, dried under programmed temperature and humidity, then calcined at 500 degrees C to remove organics. Grazing incident XRD verified that the zirconia membrane was partially transformed to the tetragonal phase. SEM showed a uniform layer 0.15 mu m thick on top of the support. Based on nitrogen permeation, the flow-average pore diameter of the ZrO2 membrane was estimated near 3.6 nm. The pore size distribution of unsupported zirconia was measured from nitrogen adsorption/desorption indicating two modes, centered at 1.5 and 3.6 nm, respectively. TEM revealed that the particle size of zirconia ranged from 5 to 10 nm. Our results illustrate that ZrO2 layer is the closed-packing of nano-size spherical particles. Supported zirconia membrane was tested by a cross-flow ultrafiltration. The rejection of soybean oil/hexane solution achieved 37% which was much better than that of bare disc.