The change of atomic structures and compositional ratios by isochronal annealing of Ag–Ni binary adsorbates at the Si(111) surface has been studied by means of LEED-AES-RBS techniques at temperatures from 200°C to 700°C. It is found that the surface coverage of Ni deposited on the Si(111)−√3 × √3−Ag surface decreases to 0 ML on annealing at 250°C for 15 min, while the Ag surface coverage is not changed by Ni deposition and subsequent annealing up to 350°C. It is also found on annealing at 350°C that Ag on the Si(111)−√19 × √19−Ni surface produces the √3 × √3 LEED pattern and the Ni coverage by AES decreases to 0 ML. These results indicate that Ag and Ni atoms are not bound to each other on the Si(111) surface, and that Ag atoms preferentially occupy the surface with forming the √3 × √3−Ag structure and Ni atoms dissolve into the Si bulk. Moreover, it is found that the room temperature deposition of Ni onto the Si(111)−3 × 1−Ag surface produces a mixed structure of √3 × √3 and 3 × 1, which is changed into the single √3 × √3 structure by subsequent annealing at 200°C. It indicates that Ag atoms move from the 3 × 1−Ag site into the √3 × √3−Ag site due to the co-existence of Ni adsorbates.