The resonance light scattering (RLS) of acridine orange (AO) are greatly enhanced by both nucleic acid and cetyltrimethyl ammonium bromide (CTMAB). Based on this, nucleic acids can be sensitively determined. The interaction of AO with nucleic acid in the presence of CTMAB is studied by using RLS, absorption spectroscopy, zeta potential assay, transmission electron microscope (TEM) image and molecular molding. On its surface, nucleic acid acts as the template to promote the assembly of both AO and CTMAB in close proximity, which formatted large AO-nucleic acid-CTMAB association. Therefore, RLS intensity of cationic dye is greatly enhanced. (C) 2003 Elsevier Science B.V. All rights reserved.