For surface modification of polymers with hydrophilic functional groups, acrylic acid was grafted and immobilized on the surface of polyethylene(PE) by cold-plasma treatment using Ar gas. The modifications were identified by analysis of ATR-IR spectrum and by the measurement of contact angles. Compared to virgin PE, significant decreases in contact angle were observed for both the grafted PE and the immmobilized PE. The decreases of contact angle were in the range of 47∼53° for grafted PE and 23∼26° for immobilized PE. The degree of hydrophilicity depended strongly on the plasma-treating time and discharge power. For the case of grafting it has shown that the longer plasma-treating time, the higher hydrophilic character. For the case of immobilization, whereas, higher discharge power and longer exposure to plasma have shown the detrimental effect for the preparation of hydrophilic PE surface due to the decrease of carboxyl group by ablation effect. The decrease in adhesion strength of immobilized PE, compared to grafted PE, was also attributed to the ablation of carboxyl group.