Microstructures and properties of alumina ceramics are sensitive to sintering additives, and commercially available readyto-press alumina powders may not contain required sintering additives for specific applications. We show a simple and practical way of microstructure design of alumina ceramics made from the commercial powders through surface modification. The method utilizes the micro-porous feature of an alumina green body pre-sintered at 1000°C, and deposits ultra-low-density sintering additive slips onto the micro-porous substrate. The surface microstructures can be refined if an ultra-low-density MgO or SiO 2 slip is deposited onto the substrate, whereas a TiO 2 slip leads to coarser and extended grain structures. TiO 2 /MgO, SiO 2 /MgO, and TiO 2 /SiO 2 combinations have also been tested, so that various surface modifications can be achieved. Fig. 2. X-ray diffraction pattern of the alumina modified with TiO 2 /MgO slip.