An inductively-coupled H2O vapor plasma was used to modify the surface of polycarbonate and polyethylene terephthalate track-etched membranes with the goal of permanently increasing the hydrophilicity of the membrane surfaces. Contact angle measurements on freshly treated and aged samples confirmed the wettability of the membrane surfaces was significantly improved by plasma treatment. X-ray photoelectron spectroscopy and scanning electron microscopy analyses revealed increased oxygen incorporation onto the surface of the membranes, without any damage to the surface or pore structure. Contact angle measurements on a membrane treated in a stacked assembly suggest the plasma effectively modified the entire pore cross section. Plasma treatment also increased water flux through the membranes, with results from plasma modified membranes matching those from commercially available hydrophilic membranes (treated with wetting agent). Mechanisms for the observed modification are discussed in terms of OH and O radicals implanting oxygen functionality into the polymers. ► The surfaces of track-etched membranes were modified using H2O vapor plasmas. ► The entire membrane cross section was undamaged and became permanently hydrophilic. ► Modified membranes have significantly higher water flux than untreated membranes. ► Modification occurs via substantial oxygen incorporation in the treated membranes. ► Mechanisms for observed changes in membrane composition and performance are given.