Abstract:The study on localization of ATP-ase in root nodules of Astragalus sinicus and Sesbania cannabina shows that the particles of lead phosphate precipitates resulting from the reaction of ATP hydrolytic enzyme are distributed in cell wall, plasmolemma, cytoplasm and peribacteroid membranes etc. of the host cells. This ATP-ase plays an important role in the transportation and absorption of substances. Owing to the need of photosynthates provided for the nitrogen fixation of root nodules, the active reaction of ATP-ase in bacteroids varies with their developments. The numbers of bacteroids having ATP hydrolytic enzyme in young root nodules are significantly less than those in senescent nodules. Possibly, this active reaction is related with the physiological function of nitrogen fixation of bacteroids at different development stages.