Responsive polymer interfacial materials are ideal candidates for controlling surface wetting behavior. Here we developed smart nanostructured electrospun polymer membranes which are capable of switching oil/water wettability using CO2 as the trigger. In particular, the combination of CO2-responsiveness and porous nanostructure enables the as-prepared membranes to be used as a novel oil/water on-off switch. We anticipate that the promising versatility and simplicity of this system would not only open up a new way of surface wettability change regulation by gas, but also have obvious advantages in terms of highly controlled oil/water separation and CO2 applications.