Abstract: Sixteen cDNA fragments of Phaeodactylum tricornutum were isolated and identified to be up-regulated under nitrogen starvation by suppression subtractive hybridization (SSH) technology in order to elucidate the molecular mecha-nism of the diatom nitrogen utilization. Seven of them have high similarity with the functional genes related to the utiliza-tion of nitrogen. Northern blotting analysis indicated that 5 genes, nitrate transporter gene (nrt), nitrite reductase gene (nir), ammonium transporter gene (amt), ATP-binding cassette transporter gene (abc), and purine permease gene (pup), were significantly up-regulated under nitrogen starvation.