||In this experiment, the surface morphology of Ag(111) with deposited Sb was studied by ultra-high vacuum scanning tunneling microscopy (UHV-STM). It was reported previous that Sb acts as a surfactant in the homoepitaxy of Ag(111) and changes the growth mode from 3-dimensional to 2-dimensional. The goal of this experiment is to learn how the Sb atoms are incorporated on the Ag(111) surface with the aim of understanding the surfactant action of Sb. According to the atomically-resolved images, most of the Sb atoms are incorporated onto the Ag(111) surface in substitutional sites at room temperature, with preference to form patches of Ag2Sb surface alloy with ([square root]3 x [square root]3)R30° periodicity. With 0.02 to 0.3 monolayer (ML) Sb deposition, these structures were observed both on the flat surface and also in the form of monolayer islands. After ~300°C annealing, patches at step edges disappeared and the Sb atoms started to have a more uniform distribution except at the step edges which were decorated by a single chain of Sb atoms. This chain may play an important role in the surfaclant effect in homoepitaxial growth of Ag(111). Annealing also promoted the formation of straight step edges along the (211) direction. Sb seemed to affect the mobility of Ag atoms along the step edges. In the experiment of 135°C annealing on 0.1ML Sb-Ag, we observed that it induced the formation of interesting "dark lines" along the (110) direction linking Sb atoms at the lower terraces of the step edges. These lines were displaced by about four Ag-Ag separations (11.52ÅA±0.31ÅA) from the step edges along an equivalent (110) direction. The reason for the formation of these dark lines is still unknown.