Nitrogen is one of essential nutrients for plant growth.Under the N deficiency at different time points，the dynamic changes of the expression of genes and activity of enzymes related to nitrogen assimilation in rice were investigated.The results showed that the concentrations of ammonium and nitrate significantly reduced under the N deficiency.Under the N deficiency for a short time，the expression level of genes including NR1, NR2, NiR2,GS2,Fd-GOGAT,GDH2,GDH3 in the shoots as well as NR1,NR2,GDH4 in the roots were up-regulated,and then their expression level decreased after a long time under the N deficiency.Along with the extension of time under the N deficiency,the GS,Fd-GOGAT activities in whole plants,NR activity in shoots and NADH-GOGAT activity in roots decreased while the NADPH-GDH activity in shoots increased.In roots the activities of NR,GDH increased at first and then decreased，while in shoots the NiR activity was just the opposite.Re-supplied N after 7 days of N deficiency,the transcriptional expression level and enzyme activities of NR,NiR,GS,GOGAT,GDH restored,and expression level of some genes increased as well.