Porous silicon (PS) with different porosity was obtained by anode electrochemical etching of boron-doped Si (100); the as-etched samples were then covered with Fe films by magnetron sputter technique. Analysis of surface profile and structural investigation were done by scanning tunneling microscopy and X-ray diffraction. Magneto-optical Kerr effect was employed to measure the hysteresis loops of the iron films sputtered onto PS and the reference sample on the Si substrate. The coercivity of the PS-based Fe films is larger than that of the Si-based ones, and increases with the porosity of the PS substrate. As for the PS-based samples with the same porosity, the coercivity of Fe films decreases with their thicknesses in a certain range. We found that the spongelike structure of PS can be effectively used to control the coercivity of iron films on the PS substrates.