The morphological changes in the UHMWPE fiber surface with the oxygen plsama treatment were observed and characterized. The surface morphology of the fiber was observed with scanning electron microscope(SEM) and atomic force microscope(AFM) as the plasma treatment condition varied in power and time. To obtain the quantitative information for the morphological changes, the pore area of the fiber was measured with the mercury porosimeter. By the oxygen plasma treatment, a number of pit-shaped micropores were produced on the fiber surface perpendicular to the fiber axis direction, and they were changed with the plasma treatment level. In AFM images, the surface morphology was altered from a somewhat smooth feature to the more rough and complex one as the level of plasma treatment. From the results of the mercury porosimetry, the changes in the pore generation by the plasma treatment were observed in the region below the pore diameter of 0.3 $mu$m mainly Due to the severe etching effect, the higher level of the plasma treatment of 150W cause the larger scale pores over the pore diameter of 0.3 $mu$m to 0.8 $mu$m on the fiber surface. As a consequence, total pore area of the fiber was increased within the relatively low treatment level and decreased with the higher level of treatment power of 150W after showing a maximum value at 100W for 5 minutes.