We have investigated Sb overlayer structures on Si(111) with low energy electron diffraction and scanning tunneling microscope (STM). The Sb/Si(111)-5 root 3 X 5 root 3 structure was constructed via the desorption of Sb from the saturated 2 X 1 surface at elevated temperature (700-750 degrees C). Its atomic structure and formation process were extensively studied with STM images, considering the structural stability. This Sb structure could be described in terms of the site selective replacement of outermost Si atoms with Sb atoms in the dimer-adatom-stacking fault 5 X 5 structure, which is generated by both the saturation of dangling bends and strain due to the large lattice mismatch.