A simplified method for forming a palladium circuit pattern on polyimide resin substrate was proposed. The carboxyl group, as a cation exchange group, was formed on the polyimide resin surface by a potassium hydroxide treatment. Palladium(II) ion was then adsorbed onto the surface modified polyimide resin by ion exchange. Ultraviolet irradiation of this palladium(II) ion absorbed resin with sodium formate coated on its surface resulted in the formation of a palladium thin film. Irradiation through a metal-on-quartz mask onto the modified polyimide resin surface photoreduced the palladium ion into metallic palladium circuit patterns easily without using a plating resist.