Physical properties of advanced ceramics are influenced by impurities produced in the forming process. The forming compacts produced by slip casting using gypsum molds contain calcium and sulfur in green bodies. Therefore, a porous Al2O3-glass mold was produced and slip casting was performed in the present study. Porous Al2O3 ceramics as casting molds were examined in comparison with gypsum mold from viewpoints of free energy for wettability and rate of filter cake buildup. The sintered compact of Al2O3 produced by slip casting using the porous Al2O3-glass mold was compared with those using the gypsum mold. Transmittance of the sintered Al2O3 compacts using the porous Al2O3-glass molds was increased in comparison with that using the gypsum mold.