Ion beam and thermally-induced interface reactions between highT_c superconducting thin film of Y₁Ba₂Cu₃O_7−x and metal overlayer of Ag are studied with a view to control the interfacial property of contact resistance. The interface reaction is induced by 100 keV Ar⁺ ion beam with different ion dose values ranging from 5 × 10¹³ to 3×10¹⁴ ions/cm². The YBaCuO film-metal interface is characterized by using the small angle XRD to study the structural properties of the interfacial phases. The electrical property of the interface, specifically contact resistance, has been investigated for different dose values and thermal treatments. Three-probe vs four-probe configuration has been adopted to measure the contact resistance.