Low-temperature deposition of α-Al₂O₃ film is the key to expand its industrial applications. Al, α-Al₂O₃ and Al + 15wt% α-Al₂O₃ targets were used to deposit alumina films on Si(100). The as-deposited films by radio frequency magnetron sputtering (RFMS) were analyzed by grazing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and the nano-hardness was measured by depth-sensing indentation method. The results show that the single phase α-Al₂O₃ films were successfully deposited by reactive sputtering the Al+α-Al₂O₃ composite target at 550 ℃. When deposited at the substrate temperature of 550 ℃, the α-Al₂O₃ sputtered from the target preferentially form α-Al₂O₃ nucleus which could suppress the formation of γ phase, and promote the homoepitaxial growth of the α-Al₂O₃ to obtain the single phase α-Al₂O₃ films.