Palladium (Pd) line patterns were formed on glass and polyimide substrates by thermal decomposition of coated palladium acetate (PdAc) film using an argon ion laser. We studied the effects of substrate material and PdAc film thickness on light absorption, Pd pattern features, and size. PdAc film less than 250nm thick had low light absorption less than 5%, making direct decomposition by laser irradiation difficult. With such thin palladium acetate film, no Pd pattern was formed on glass substrates, because the Ar laser beam was almost transparent through the glass. The polyimide substrate, 50μm thick, showed high light absorption of about 95%, indicating easy heating by laser irradiation. The Pd patterns were formed, independent of PdAc film thickness, because the film was heated by thermal conduction from the substrate. Smooth, flat Pd features were formed at laser power densities of 1.5-3.5kW/cm² that narrowed with decreasing PdAc thickness. Pattern widths were 1-2 times the laser beam diameter.