In pH 7.0 tris-HCl buffer solutions and in the presence of 0.017 mol?L-1 NaCl, herring sperm DNA was combined with gold nanoparticles in size of 10 nm to form stable complex, and the NaCl did not cause the aggregation of the gold nanoparticles. Upon addition of Hg2+, that reacted with DNA to form more stable complex of Hg2+-DNA, and the gold nanoparticles aggregated to from larger nanogold clusters that led to considerable enhancement of the resonance scattering intensity at 572 nm enhanced considerably. The effect of GN concentration, DNA concentration, NaCl concentration, incubation time, and temperature, and ultrasonic irradiation was considered respectively, the conditions of 3.87 μg?mL-1 GN, 11.7 μg?mL-1 DNA, pH 7.0 Tris-HCl buffer solutions, 17 mmol?L-1 NaCl, and incubation 10 min at 37 ℃ under the ultrasonic irradiation were chosen for use. Under the conditions, the enhanced resonance scattering intensity at 572 nm was linear to the Hg2+ concentration in the range of 3.3-3 333.3 nmol?L-1, with regress equation of ΔI572 nm=0.019c+5.0, coefficient of 0.999 1, and a detection limit of 2.5 nmol?L-1 Hg2+. Results of interference tests showed that 30 μmol?L-1 Mn2+, 33 μmol?L-1 Mg2+ and Zn2+, 100 μmol?L-1 Cd2+, 200 μmol?L-1 Fe3+, and 420 μmol?L-1 Mo6+, Pb2+ and Cu2+ did not interfered with the determination of 0.33 μmol?L-1 Hg2+. That is, this resonance scattering spectral assay is of good selectivity. This assay was applied to the detection of Hg(Ⅱ) in water sample, with a relative standard deviation of 5.1%, and the results were in agreement with that of the cool vapor atomic absorption spectrophotometry.