Polycrystalline copper and gold surfaces eroded by Argon ion bombardment were examined by a field emission scanning electron microscope to study the sputtering processes. Argon ion beams of about 3 keV to 15 keV were supplied from Edward type and duoplasmatron type ion guns. The observation suggests that the development of surface erosion with the increasing ion dose resulted at first in conical holes or craters and then these craters became larger to join with each other to produce a cone in the midst of coupled craters or at the inner wall of craters with further irradiation. Further bombardment resulted in a jumble of cones and finally revealed the grains which had smooth but shallow scoped surfaces. These features were common for both polycrystalline gold and copper surfaces mechanically or electrolytically polished.