Transparent alumina were tentatively prepared by spark plasma sintering, using aggregated submicrometer-sized commercial Al(2)O(3) powder. It is found that the pretreatment of the powder in hydrofluoric acid significantly reduces the aggregate size of the powder, suppresses the grain growth, and improves the microstructure homogeneity of the sintered ceramics. The sample sintered from the pretreated powder is highly transparent, while the sample sintered from the untreated powder is translucent at most. The fundamental reasons for this are investigated.