A variety of plasma treatments have been employed to achieve permanent hydrophilic surfaces throughout the membrane structure. Specifically, we have modified microporous polyethersulfone (PES) membranes using H2O, CO2, and N2 plasma treatments to implant polar functional groups; alternatively, Ar-plasma treatment followed by grafting of hydrophilic monomers (acrylic acid and acrylamide) in the vapor phase has also been successful at modifying PES membranes. PES membranes treated with H2O and CO2 plasmas as well as the grafted membranes are found to be permanently hydrophilic (for a minimum of six months), and the entire membrane cross-section is modified. Chemical changes to the modified PES membranes were determined with FTIR and XPS measurements. Furthermore, water bubble point measurements and electron microscopy results reveal that pore sizes of the modified membranes are only slightly affected, depending on the treatment. Incorporation of polar functionalities results in an increase in the glass transition temperature (Tg) and a moderate change in tensile strength of the modified membranes. Most importantly, the surfaces of the modified membrane are less susceptible to absorption by bovine serum albumin (BSA) proteins.