Equilibrium between vapor pressure of water and moisture content of rice grains for sake making was studied. Polished or unpolished rice grains were stored in sealed bottles at 1.7°, 11.4° and 27.6° over 24 hr, and relative humidity of gaseous phase and moisture content of grains were measured. The relationship among vapor pressure (P), moisture content (W) and temperature (T) could be expressed in the following equation: W=10-(0.01711+0.943)×P1/(-0.0127T+2.267) Cultivars and polishing degree of rice did not affectthe results.