In order to clarify nitrogen uptake and metabolism of rice roots on a molecular basis, studies by means of quantitative real-time PCR were carried out on expression of nitrogen absorbing and metabolizing genes in relation to different ammonium/nitrate ratio in treatment.The results show that (1) in terms of expression level, OsAMT1.1 among N absorbing genes, OsGln1.1 among GS genes and OsGlu among GOGAT genes was the highest; (2) Significant up-regulation by ammonium and down-regulation by nitrate were found in the expression of OsAMT4 1, in any treatment whereas significant nitrate-depressed expression for OsAMT1.1, OsAMT1.2, OsAMT1.3 and OsNRT2 was observed when the ratio of ammonium to nitrate varied from 100:0 to 50: 50, and significant nitrate-induced expression for OsAMT1.2 and OsAMT1.3 when the ratio of ammonium to nitrate varied from 50:50 to 0:100; (3) Among the genes coded as GS, OsGln1.1 were significantly up-regulated by nitrate and down-regulated by ammonium, significant nitrate-induced expression for OsGln2 and nitrate-depressed expression for OsGln1.2 when the ration of ammonium to nitrate varied from 100:0 to 50:50; (4) Among the genes coded as GOGAT, OsGlt1 and OsGlu showed no significant variation in the process of the ratio of ammonium to nitrate varying from 100:0 to 50:50, but were significantly down-regulated with the ratio of ammonium to nitrate further varying from 50:50 to 0:100; significant up-regulation by ammonium and down-regulation by nitrate were found in the expression of OsGlt2; (5) In general, the regulation of expression of these genes by ammonium and nitrate depends on the ratio of ammonium to nitrate in the primary solution where the rice grew.