The asymmetric hybrid membranes of polyethersulfone (PES) and $ZrO_2$ nanoparticles were prepared via new one-step procedure combining simultaneously the phase-inversion method and the sol-gel technique. The optimum contents of $Zr(PrO)_4;and;HNO_3$ catalyst were determined by the adsorption experiments of phosphate anion onto the resulting hybrid membranes. The maximum adsorption of phosphate anion is obtained at the conditions of 0.15 mL $Zr(PrO)_4$ addition per 1 mL PES and 30 mL $HNO_3$ addition per 1 mL $Zr(PrO)_4$. Variation of morphology, performance and incorporated $ZrO_2$ amount of the resulting hybrid membranes were discussed and determined using SEM, pure water flux, TGA, ICP, XRD and contact angle measurements. Increasing $Zr(PrO)_4$ addition into casting solution, pure water flux is increased and $ZrO_2$ amount in the hybrid membrane is maximized at the conditions 0.15 mL $Zr(PrO)_4$ addition per 1 mL PES. The prephosphatation of PES-$ZrO_2$ hybrid membrane was studied to modify the surface characteristics of membrane. Ultrafiltration of bovine serum albumin (BSA) solution was performed in a dead-end cell using both a bare (non-phosphated) and a phosphated hybrid membrane. It is revealed that both the permeate flux and BSA rejection were increased as about 40% by prephosphatation of hybrid membrane. These results may be explained on the basis of the increase of membrane hydrophilicity, which was determined from contact angle measurements.