High precision glass molding technology has been applied for manufacturing a highly accurate optical element such as glass aspheric lens. In this paper, cemented carbide system and silicon carbide system used as the mold material are introduced. The change of surface condition under the high temperature and workability of these mold materials are discussed. Existence of cobalt affects the stability of surface condition at high temperature in cemented carbide system. Silicon carbide had excellent surface stability compared with cemented carbide. The workability of mold material, which means if good surface condition of material can be obtained and if material can be readily removed after grinding and polishing, is affected by grain size of grindstone, working condition and kinds of material. In particular, the crystal orientation in silicon carbide causes the difference of workability.