α-Al2O3 platelets were successfully synthesized in molten NaCl-KCl salt using the pre-calcined Al(OH)3 powders as starting materials, and the effect of milling medium on the powder characteristics was investigated, with the purpose of obtaining high performance sintered ceramics. When anhydrous alcohol was used as milling medium, the synthesized product at 900°C was porous α-Al2O3 with a small amount of amorphous Al2O3. While deionized water was used, single-phase and dense α-Al2O3 platelets were developed at 900°C. It was related with different solubility of NaCl-KCl salt in anhydrous alcohol and deionized water during milling. When the synthesized α-Al2O3 platelets were used as seeds in sintered ceramics, fracture toughness was developed.