Anti-fouling and anti-bacterial polyethersulfone (PES) membranes were developed by the addition of poly(2-dimethylaminoethyl methacrylate) grafted silica nanoparticles (SiO₂-g-PDMAEMA NPs) and further post-quaternization. The SiO₂-g-PDMAEMA NPs were first synthesized by grafting PDMAEMA brushes from SiO₂ NPs via surface-initiated, reversible addition fragmentation chain transfer (RAFT) polymerization. PES/SiO₂-g-PDMAEMA hybrid ultrafiltration (UF) membranes were then prepared from the blending solutions of PES and SiO₂-g-PDMAEMA NPs via non-solvent induced phase separation (NIPS) process. The PDMAEMA chains incorporated into the PES membranes were further quaternized by reacting with 1,3-propane sultone (1,3-PS) and methyl iodide (CH₃I), respectively. After treatment with 1,3-PS, the resulting zwitterionic PES membranes exhibited excellent hydrophilicity, water permeability, solute rejection and protein anti-fouling properties. The cationic membranes obtained from CH₃I treatment showed strong anti-bacterial activity against Escherichia coli (E. coli) and Staphyloccocus aureus Rosenbach (S. aureus). This work presents a convenient strategy for anti-biofouling modification of polymer membranes via surface quaternization of the reactive SiO₂-g-PDMAEMA NPs additive.