In this study, the preparation and properties of polysulfone (PSf) ultrafiltration (UF) membranes with sulfobetaine polyimides (PIs) as blending additive were reported. Three molecular weights sulfobetaine PIs were synthesized and blended with PSf to fabricate UF membranes via non-solvent induced phase separation process. It was proved that membrane hydrophilicity, porosity and antifouling properties were significantly enhanced due to the introduction of sulfobetaine PI. More importantly, these sulfobetaine PI/PSf blend membranes exhibited extraordinary thermal stability. It showed that surface hydrophilicity and chemical structures of the blend membranes remain stable after being kept in 90 degrees C water bath for 3 h. Experimental results indicated that the addition of sulfobetaine PI substantially promoted the overall performances of PSf membranes, such as pure water fluxes (PWF) (270.2 vs. 140.4 L m(-2) h(-1)), bovine serum albumin (BSA) rejection (95.2% vs. 86.9%), flux recovery ratio (FRR) (93.3% vs 60.4%), etc.