The Sb adsorption process on the Si(111)-In(4x1) surface phase was studied in the temperature range 200-400 o C. The formation of a Si(111)-InSb (2x2) structure was observed between 0.5 and 0.7ML of Sb. This reconstruction decomposes when the Sb coverage approaches 1ML and Sb atoms rearrange to (3x3) and (2x1) reconstructions; released In atoms agglomerate into islands of irregular shapes. During the phase transition process from InSb(2x2) to Sb(3x3) (θ S b >0.7ML), we observed the formation of a metastable (4x2) structure. Possible atomic arrangements of the InSb(2x2) and metastable (4x2) phases were discussed.