Abstract: The physiological diversity in roots of different early rice varieties under high temperature stress during the period of the grain filling was studied. The res ults indicate that the roots activities of SOD, POD and CAT are influence d by the high temperature respectively, and the impact on the variety of heat resistance is less than that of the variety of heat sensitivity. Under high temper ature stress, the activities of protecting enzyme in roots of the variety of heat resistance can be renewed rapidly to the level of its antitheses. The _α-NA oxidation capacity in roots of the variety of heat resistance is not affected by the high temperature stress, but that of the variety of heat sensitivity decreases obviously. Therefore, the _α-NA oxidation capacity in roots can be considered as a guide line of the rice roots to high temperature resistance.