Abstract: The activities of nodule average nitrogen-fixing and NR of 1-year-old Alnus cremastogyne seedlings reached its maximum in late May,which were 11.03μmol C2H4/(gFw·h)and 0.89μmol NO2-/(gFw·h) respectively.When the nodule began senescence in June,both of them decreased rapidly,but the nodule average GS activity increased.The weight of the adult nodule and the old nodule of the 2-year-old seedling was 70% more than its total nodule weight.The ratio of the adult nodule weight to the total nodule weight per seedling was the highest in late May and that of old nodule was the highest in June,they were 51.4% and 82.1% respectively.When the nodule developed from the juvenile to theadult and then to the old,the nitrogenfixing activity decreased with the increase of the GS activity.The NR activity was the highest in the adult,middle in the old and lowest in the juvenile.With the development of nodule,the mitochondria of the host cell decreased,and finally disappeared in the old,the vesicle size decreased but its number increased,and the vesicles connected tightly to each other,forming a regular structure.The characteristics of nodule cell ultrastructure was discussed,which might have something to do with the three nitrogen assimilation enzymes in the nodule.