Porous meshes with superhydrophilicity and underwater superoleophobicity have attracted much attention for oil/water separation. In this work, poly(sulfobetaine methacrylate) (PSBMA), was co-deposited with polydopamine (PDA) to cover steel meshes and to endow them with characteristics for oil/water separation. Compared with PDA-modified meshes, the oil contact angle increases to 158.6 ± 8.0° and the sliding angle decreases to 3.9° for the PSBMA/PDA-modified ones, indicating superoleophobic behaviour underwater and ultra-low adhesive properties towards oil. These results are mainly attributed to the superhydrophilicity of PSBMA and the highly rough surface morphology in micro-nanoscale introduced during the co-deposition process. The PSBMA/PDA-modified meshes show excellent performance in gravity-driven oil/water separation. They are stable towards organic solvent treatment, and retain the wettability in sea water for a long time. This one-step PSBMA/PDA co-deposition method provides a convenient and effective approach to modify porous materials with underwater superoleophobicity for oil/water separation.