In order to improve the ultrafiltration performance of polyvinylidene fluoride （ PVDF） membrane,hybrid PVDF/Al₂O₃ membranes with different Al₂O₃ contents were prepared via the in-situ polymerization of aluminium isopropoxide （ AIP） and PVDF in a sol-gel process. Then,the structure and properties of the prepared hybrid membranes were characterized by means of SEM,IR,ultrafiltration experiments,contact angle test and mechanical test. The results indicate that there exist alumina polymers in the prepared membranes due to the hydrolysis polymerization of AIP in PVDF,and that,at an AIP dosage of 12% ,the pure-water flux of the prepared hybrid membranes increases by 83. 36% ,the BSA （ Bovine Serum Albumin） retention rises from 88. 27% to 96. 64% ,and the hydrophilicity,mechanical properties and pollution resistance of the membranes are all significantly improved.