Transparent and porous boehmite, γ-Al2O3 (500°C) and θ-Al2O3 (900° and 1000°C) thin sheets (50–100 μm) have been prepared from boehmite sols. γ-Al2O3 shows about 48% porosity and 292 m2/g surface area. On transformation from γ-Al2O3 (500°C) to θ-Al2O3 (900°C), the porosity still remains high, i.e. ∼45%; however, the surface area becomes 138 m2/g. The porosity and surface area of θ-Al2O3 become about 41% and 97 m2/g respectively on further heating to 1000°C. A gradual increase of average pore radius during this thermal treatment suggests that coarsening of the pore occurred during the densification process. Both γ-Al2O3 and θ-Al2O3 show high degree of transmission from UV to NIR wavelength region. Cerium exists in +4 oxidation state in the boehmite as well as in the γ- and θ-Al2O3. The ultraviolet absorption edge of the alumina was tailored by varying the concentration of cerium.