The size distribution and changes of volume and grain hardness of `Sedohadaka`, waked barley of various polishing yields during hydration process at various temperatures were investigated, and were analyzed kinetically, Both major and minor diameter of barley grain decreased linearly during polishing, and the decreasing rate of major diameter was greater than that of minor diameter. The volume change of barley grain could be expressed as a power of hydration time, and a break point was found in case of non-polished barley. The changing rate of grain hardness followed the equation of a first-order reaction, and the reaction rate constant increased with decreasing polishing yields and at higher temperature in the range of 20∼60℃. The activation energy of hardness change reaction of polished barley during hydration were ranged 5.1∼7.8㎉/mole, and 13.3㎉/mole of non-polished barley.