A series of oil/water separation membranes with tunable surface wettability based on poly(ionic liquid)s (PILO were prepared via a facile one-step photopolymerization of N-vinylimidazolium ionic liquids and divinylbenzene on meshes. The wettability of PIL-based membranes (PILMs) was adjusted by the structures of PILs, specifically the alkyl chain length of imidazolium (butyl and octyl) and anion species (acrylic anion, Br-, and PF6-). Tunability of wettability resulted in the hydrophilic or hydrophobic property of PILMs. The hydrophilic poly(1-vinyl-3-butylimidazolium acrylate)-based membrane (PILM-1) transported water and intercepted oil, while the hydrophobic poly(1-vinyl-3-octylimidazolium hexafluorophosphate)-based membrane (PILM-5) removed oil and rejected water. The two membranes with opposite wettability showed excellent oil/water separation efficiency (above 99%) in batch processes. Continuous oil/water separation was also achieved by assembling PILM-1 and PILM-5 on the fabricated devices. A T-type device could separate various oil/water mixtures continuously, and a tank-type device could separate dispersed oil/water mixtures, with a handling capacity of 46 L within 12 h.