Recent outbreak of Severe Acute Respiratory Syndrome (SARS) that caused almost 800 victims requires a development of efficient inhibitor against SARS coronavirus (SCV). In this study, RNA aptamers against SCV NTPase/Helicase (nsP10) were isolated from RNA library containing random sequences of 40 nts using in vitro selection technique. Nucleotide sequences of enriched RNA aptamer pool (ES15 RNA) contain AG-rich conserved sequence of 10-11 nucleotides [AAAGGR(G)GAAG; R, purine base] and/or additional sequence of 5 nucleotides [GAAAG], which mainly reside at the loop region in all the predicted secondary structures. Isolated RNAs were observed to efficiently inhibit double-stranded DNA unwinding activity of the helicase by up to similar to 85% with an IC50 value of 1.2 nM but show a slight effect on ATPase activity of the protein in the presence of cofactor, poly (rU). These results suggest that the pool of selected aptamers might be potentially useful as anti-SCV agents. (c) 2007 Elsevier Inc. All rights reserved.