Abstract: The effects of 4PU-30 on the leaf senescence and rato ning buds germination during the ripening stage of hybrid rice were studied．The results indicate that the rice leaves treated by 4PU-30 5 days after full heading can delay the degradation of the cholorophyll，increase the activities of superoxide dismutase and decrease the content of MDA and the rate of electrolyte leakage，postpone the leaf senescene efectively，improve the root vigour，promote sprouting and growing of ratoning buds and increase the buds survival rate．