In order to clarify the mechanism of frost injury of barley varieties, the authors investigated in the field ( 1 ) the changes of air temperature at 3, 15, 50, 100 and 150 cm above soil-surface ; ( 2 ) the temperatures of leaf and stem ; and ( 3 ) the progress of frosting on leaves ; with the intervals of one hour or thirty minutes from 1.00 to 8.OO a.m. The results obtained were follows : ( 1 ) For the vertical distribution, the air temperature was the lowest at the height of 15 cm above soil-surface during the tested period. ( 2 ) For the plant temperature, the temperature of leaf was Idwer than that of stem before sun-rise but higher after sun-rise. Moreover, the leaf temperature showed the lowest temperature among all: the temperature measured. The air temperature above the plant-surface was between the leaf temperature and the stem temperature at any time. ( 3 ) In the course of frosting, it dewed finely on leaves first of all, and the dew drops were presently frozen. Before long, the frozen dew drops grew to frost, and the color of leaves changed to, dark green with the progress of frosting. Remarkable varietal differences of frost quantity on leaves were recognized, that is, "Nami", type vras severely frosted, while "Uzu" type was slightly frosted.