In order to improve the antibacterial and antifouling properties of polyimide (PI) membrane, both silver nanoparticles (AgNPs) and zwitterionic sulfobetaine methacrylate (SBMA) are grafted onto PI membrane surface via a two–step modification route. The reaction mechanism involved, as well as changes in the membrane morphology and surface properties are investigated via various characterization techniques. The antibacterial performance is assessed by the zones of inhibition and bacterial suspension immersion tests. The antifouling property of the modified membrane is evaluated via the filtration test using the bovine serum albumin (BSA) and dodecyl trimethyl ammonium bromide (DTAB) aqueous feed solutions. The results show that, the modified PI membrane exhibits significantly improved antibacterial and antifouling performances simultaneously.