Poly(ethylene terephthalate) (PET) fiber knit-fabrics were irradiated by glow-discharge plasma (GDP) at one-atmosphere, then subsequently grafted with a hydrophilic acrylic acid (AA). Degradation of GDP-treated surface was determined by weight loss ratio. This degradation is proportional to time of exposure. The wicking-time method was used for roughly estimating hydrophilic durability of grafted surfaces versus the time of exposure and times of washing. On the grafted surface, characterized by X-ray photoelectron spectroscopy (XPS), carbon contents C_1s decreased while oxygen contents O_1s considerably increased. This results in an amount of oxygen polar functional groups like carboxylic (O−C^*=O) and carbonyl (C^*=O) groups introduced into the grafted surface. Grafted surface morphology observed by scanning electron microscopy (SEM) displays some large area of corn-structure compared to relative smooth morphology of the control fabric. It also suggested that hydrophilic improvement was closely related to oxygen containing functional groups incorporated onto the grafted fiber surface and the surface roughness.