A new label-free resonance light scattering method for the highly selective and sensitive detection of mercury ion was designed. This strategy makes use of the target-induced DNA conformational change to enhance the resonance light scattering intensity leading to an amplified optical signal. The Hg2+ ion, which possesses a unique property to bind specifically to two DNA thymine (T) bases, in the presence of Hg2+, the specific oligonucleotide probes form a conformational reorganization of the oligonucleotide probes from single-chain structure to duplex-like complexes, which can greatly enhance the resonance light scattering intensity. Under the optimum experimental conditions, the enhanced resonance light scattering intensity at 566 nm was in proportion of mercury ion concentration in the range 7.2×10-9～9×10-8mol·L-1 with the linear regression equation was ΔI=5.12c+3.55(r=0.999 5). This method was successfully applied to detection of Hg2+ in enviro nmental water samples, the RSD were less than 1.9% and recoveries were 99.4％～104.3％. This label-free strategy uses the mercury specific oligonucleotide probes as recognition elements and control the strength of resonance light scattering by changing the concentration of Hg2+. It translating the small molecule detection into the DNA hybridization behavior leading to an amplified resonance light scattering signal can well enhance the sensitive detection of Hg2+. With amplification by DNA hybridization behavior, the sensitivity for the detection of Hg2+ can achieve 2.16×10-9mol·L-1. In this study, the stacked T-Hg2+-Tfunctioned not only as amplification property but also as an selective recognition. The highly specific detection of Hg2+ is attributed to the formation of a stable T-Hg2+-T complex.