Electrospun fine fibers were surface-modified by surface-initiated atom transfer radical polymerization (SI-ATRP) to reform their surface character without sacrificing their bulk properties. Electrospun fibers of two types of polymers, poly(methyl methacrylate)-based copolymers and semi crystalline poly(butylene terephthalate), that have ATRP initiating units attached to them were modified by poly(sulfobetaine) brushes or fluorinated polymer brushes. The fluorinated polymer brushes make the electrospun fiber mat super-hydrophobic, whereas the poly(sulfobetaine) brushes make the electrospun fiber super-hydrophilic. These mats can be used for water/oil separation and exhibit non-fouling properties. The semi-crystalline polyester fibers keep these properties even at elevated temperatures.