A silver–polydopamine (Ag–PDA) nanohybird was used to produce polysulfone (PSf) ultrafiltration membranes with excellent antifouling and antibacterial properties. First, the catechol functional groups of polydopamine (PDA) helped with the in situ immobilization of silver (Ag) nanoparticles (<10 nm) on the PDA sphere surface; this led to the formation of the Ag–PDA nanohybrid. Then, Ag–PDA/PSf hybrid membranes were prepared via the phase‐inversion method, and the influence of Ag–PDA loading on the hybrid membrane properties was systematically investigated. When the content of Ag–PDA was 0.5 wt %, the hybrid membrane achieved optimal separation performance, including a dramatically increased pure water flux and a well‐maintained bovine serum albumin rejection. Furthermore, the Ag–PDA/PSf hybrid membranes presented a significantly enhanced protein‐fouling resistance and a good antibacterial activity. These improvements were attributed to the unique structure and properties of the Ag–PDA nanohybrid because of the synergistic effect of the hydrophilic PDA substrate and well‐distributed Ag nanoparticles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46430.