As a common IIIV compound semiconductor material, gallium antimonide （GaSb）was restricted in application due to its easy oxidation. Among all solutions, the sulfuric passivation is a common and efficient one. We chose （NH4）2S solution to study the effect of passivating process on chemical mechanical polished surface. The results were characterized by atomic force microscopy （AFM）and Xray photoelectron spectroscopy （XPS）. After passivation, Sb was further passivated compared to Ga, while the passivation level escalated when the processing period was lengthened. On the other side, longer passivation time bring severer wafer etching, which led to a higher surface roughness.