Face-centered-cubic Ag(100) submicrometer islands on an RCA-cleaned Si(100) substrate were fabricated by molecular beam epitaxy; a 500 Å Fe thin film was then grown onto Ag films at 100 °C. We experimentally demonstrate that the magnetic behavior of Fe films is strongly dependent on the thickness and morphology of the Ag underlayer. The Ag film, in order to reduce the surface free energy, forms isolated three-dimensional square islands with {111} sidewall on the Si(100) substrate. The average height, grain size and surface roughness of these Ag islands were tuned by varying the deposition thickness of the Ag film. The in-plane easy axis of the Fe film was rotated 45° while the thickness of the Ag underlayer reaches 100 Å and the Ag rough surface provides a source of domain wall pinning.