Abstract: Changes of GS activity of hybrid rice and their parent dnring growth and development were same in order,and the enzyme activity level of hybrid rice is the result of inheritance of their parent.There were significant relationship between GSactivities and several physiological and yield characters,cspecially at panicle initial stage and heading stage.Thus,we suggested that GSactivity is probably as a physiological parameter of which predict heterosis level of yield character to some extent at reproductive growth stage.