Two cDNAs encoding respectively, OsAMT1.2 and OsAMT3.3, were isolated from rice cultivars Guidan 4. The expressions of both genes in the roots of rice seedlings were induced significantly under nitrogen starvation. A yeast mutant deficient in ammonium (NH4+) transport was employed to elucidate their functional aspects. Expression of OsAMT1.2 in the yeast mutant partially complemented NH4+ uptake deficiency of the mutant cells, while OsAMT3.3 did not confer functional complementation. Relative gene expression analysis in yeast revealed a 50% lower abundance of OsAMT1.2 mRNA than the Arabidopsis AtAMT1.1, a functional NH4+ transporter characterized in the same system. Thus, the low abundant expression in the yeast system may be one of the reasons that the OsAMTs was not consequently capable for functional complementation. Our results give a clue to the consideration of using yeast for functional characterization of foreign genes in such heterologous system.