Alpha-alumina (alpha-Al2O3) materials has a wide range of applications because of its excellent properties at high temperature. Tabular alpha-Al2O3 was unexpectedly synthesized by etching mullite from SixAlyOz composites since our original intention was highly porous alpha-Al2O3. Silica-alumina xerogels with different Al/Si molar ratio as 3, 6, 9 and infinity (pure alumina) were prepared via sol-gel route, followed by calcination at 1400 degrees C to obtain SixAlyOz composites. XRD results showed that the composite existed as mullite when the Al/Si ratio equaled to 3 and as the combination of mullite and corundum (alpha-alumina) when the Al/Si ratio equaled to 6 and 9, while pure alpha-Al2O3 was obtained when Al/Si ratio equaled to infinity signed as sol-gel alpha-Al2O3. The mullite phase in SixAlyOz composites could be etched completely by hydrofluoric acid under room temperature in terms of the treating time was long enough and left tabular alpha-Al2O3 for the samples with Al/Si molar ratio as 6 and 9. The interaction between mullite and alpha-Al2O3 during the thermo process may direct the formation of tabular morphology. Structural and property characterizations show the tabular morphology, low surface area, perfect crystallinity and weak acidity of alpha-Al2O3. Furthermore, the adsorption of dibenzothiophene, a molecular with planar morphology, on tabular alpha-Al2O3, sol-gel alpha-Al2O3 as well as gamma-Al2O3 was investigated at room temperature in comparison. Tabular alpha-Al2O3 exhibited the highest adsorption capacity and best regeneration ability than other two.