For the surface modification of polymers with hydrophilic functional groups, acrylic acid is immobilized on the surface of polyethylene(PE) by cold plasma treatment using Ar gas. The identification of the immobilization is manifested by analysis of FMIR spectrum and by measurement of contact angles for the modified surface. The spectra originated from acrylic acid-modified surfaces show characteristic absorption bands of polyacrylic acid at about 1710, 1100-1300, and 800 cm(-1). Significant decreases in contact angle of plasma treated PE are observed, compared to virgin PE. The degree of the surface modification and hydrophilicity depend strongly on the plasma-treating time.