Abstract: The key technology in preparation of source core of 125I seed source was modified by plating Pd on the surface of Ag wire and then using it to adsorb 125I. One tenth mL of 1.0 g·L-1 PdCl2 solution containing HCl with mole ratio between PdCl2 and HCl of 1 to 1 was used for the plating. Values of saturation capacity of Pd on the surface of Ag wire was attained to 0.2 mg and rate of adsorption against I was attained to about 94% as determined by UV spectrophotometry. It was found that iodine was adsorbed successfully on the surface of Pd-plated Ag wire as characterized by scanning electron microscope and X ray photoelectron spectroscopy, and the adsorption was proved to be physical adsorption.