We used synthetic DNA oligos to investigate the nucleic acid chaperone properties of the N terminal domain of hepatitis delta antigen (NdAg). We found that NdAg possessed a bona fide chaperone activity. NdAg could distinguish subtle differences in the thermal stability of the base pairing region, and enabled DNA oligos to form a more stable duplex among competing sequences through facilitating strand annealing selectively, stimulating duplex conversion selectively, and stabilizing the more stable duplex. The property of NdAg identified in this study could be applied to improve the efficiency and specificity of dot blot hybridization under conditions of low stringency.