A slurry used to produce dense green compacts by slip casting should exhibit low viscosity, high solids content, and good dispersion. Slurries with good characteristics were produced in the present study by adding oligosaccharide alcohol to an Al2O3 slurry with an NH4+ salt of poly(methacrylic acid) (NH4+-PMA). The role of NH4+-PMA and oligosaccharide alcohol in the Al2O3 slurry was examined by DTA, zeta-potential measurement, high-pressure liquid chromatography, and viscometry. The viscosity of the slurry with NH4+-PMA and oligosaccharide alcohol was lower than that of the slurry with NH4+-PMA at a high solids content. Oligosaccharide alcohol did not interact with the Al2O3 surface. However, the Al2O3 slurry with NH4+-PMA was influenced by the addition of oligosaccharide alcohol. We found that the dispersibility of the slurry was greatly improved by adding oligosaccharide alcohol. The transmittance of the Al2O3 ceramics produced by slip casting using the slurry with both NH4+-PMA and oligosaccharide alcohol was higher than that of ceramics produced by slip casting using the slurry with NH4+-PMA alone. The increased optical property resulted from low viscosity, which was attributed to the addition of oligosaccharide alcohol, at a high solids content.