In this paper, nano-sized Al2O3 powders are synthesized by a thermal MOCVD (Metal Organic Chemical Vapor Deposition) combined with plasma. The effect of reaction temperature on the characteristics of the synthesized Al2O3 powders is investigated. The experimental results demonstrate that while the temperature is increased from 200oC to 1000oC, the mean diameter of Al2O3 powders reaches from 400nm to 10nm. Hence, the increment of temperature can promote the synthesis of fine Al2O3 particle. Furthermore, the powder morphologies and crystallite size are also examined by the transmission electron microscopy (TEM) and XRD. Based on TEM observation, it is found that the particles are sphere shape. The XRD analysis shows that the particles are typical γ-Al2O3 crystalline phase over 400oC. Lastly, the effect of plasma on the characteristic of Al2O3 synthesized by thermal MOCVD is also considered.