Surface modification of polycaprolactone filament has been carried out using a low pressure oxygen plasma to introduce active centers in the form of radicals, peroxides, and hydroperoxides on the surface. Evaluation by 2, 2-diphenyl-1-picrylhydrazyl method shows that there is an optimum value of exposure time, gas pressure, and discharge power for the generation of the maximum concentration of such groups. The plasma exposure time was thereafter varied to study the extent of the surface modification introduced by the plasma. It was found that only a short time of exposure to the oxygen plasma was necessary to make the surface highly wettable and polar with increased surface energy and work of adhesion. Surface chemical analysis by X-ray photoelectron spectroscopy revealed that this happens because of oxidation of the top layer of the filament, which occurs primarily by the breaking of bonds and incorporation of oxygen containing functionalities. Morphological and topographical observations by scanning electron microscopy and atomic force microscopy revealed that etching is pronounced at longer exposure times leading to a rougher surface with hill-valley features. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013