Fulllength of open reading frame sequence encoding aldoketo reductases was cloned from Nostoc flagelliforme cells with PCR. The gene was named as NfAKR. Sequence analysis showed that the complete open reading frame of NfAKR was 912 bp, which encoded 304 amino acids residues. The relative molecular mass of NfAKR was 33.51 kD, and its isoelectric point was 4.94. NfAKR protein had the aldo ket red superfamliy domain, and the threedimension structure was composed by 10 αhelices and 11 βsheets，among which there was a hydrophobic cavity as catalytic active site. Phylogenetic analysis showed that aldoketo reductase from N. flagelliforme and N. punctiforme had high similarity. Quantitative realtime PCR analysis showed that the expression of NfAKR gene was upregulated under drought stress of PEG6000.When the concentration of PEG6000 was 8%, the relative expression was 5.66, reaching the peak value. The NfAKR expression was upregulated, suggesting that aldoketo reductase plays a certain role in the process of resisting drought stress in N. flagelliforme.