The segregation kinetics and surface structures of sulfur on the Mo(111) surface have been studied by means of AES and LEED in the temperature range between 700℃ and 800℃. When the sample was heated to 800℃, sulfur segregated rapidly and progressively replaced the carbon on the surface. However, as heated to 700℃, no significant sulfur segregation has been observed. An AES analysis also showed that sulfur segregation may be controlled by its bulk diffusion rate and the presence of carbon on the surface might inhibit the surface segregation of sulfur. LEED patterns of new surfacestructures, namely Mo(111) (31/2×31/2)R30°-S and Mo(lll) l/3(99-44)-Shave beenobserved respectively.