The composite membranes of zirconium oxide-cellulose acetate were prepared in a two-step procedure combining the phase-inversion method and deposition-hydrolysis technique. The first step allowed the preparation of membranes with different morphologies, and the second step allowed a highly dispersed metal oxide to be deposited on the membranes. The XPS Ols binding energy indicated that the interaction between the oxide and the cellulose matrix is probably of hydrogen bonding type. Phosphate retentions were 75 and 90% for the composite membrane in permeation experiments. The water fluxes for a pressure of 1.7 atm were (3.7 +/- 1.7) x 10(-2) and (13.0 +/- 2.1) x 10(-2) mt min(-1) cm(-2). The membranes are very stable under continuous use. Regeneration of the membrane using NaOH 0.01 M eluent solution did not decrease significantly, ca. 10%, the membrane efficiency. The great advantage of these membranes is the low operational pressure required to obtain high phosphate retention.8713751379