In this paper, we discuss the characteristics, of diatomite, a moisture-absorbent material used for anew air-conditioning system. Diatomite powder is formed into grains (diameter: 8 mm) with a slantrotatingprocessing machine. After that, the grains are baked. Small balls (diameter: 45 mm) are thenformed from the grains, and are used as moisture-absorbent materials for cells in a moistureabsorbentdehumidifying ventilation device. Gross moisture conductivity (GMC) of the small balls wasmeasured under two conditions.