In pH 7.0 Na2HPO4-NaH2PO4 buffer solution, nanogold particles interacted with the aptamer to form a stable aptamer-nanogold complex that was not aggregation by NaCl. At 80 ℃, K+ and aptamer folded to form a stable G-quadruplex that released nanogold particles, the uncombined nanogold particles aggregated to large nanogold clusters that caused the increase in resonance scattering (RS) intensity at 563 nm in high concentration of NaCl, and the laser scattering showed that the average diameter was 120 nm. In the present paper, the resonance scattering spectral characteristics of K+-ssDNA1-Au, K+-ssDNA2-Au and K+-aptamer-Au systems were investigated, and the structural changes of aptamer were studied by circular dichroism spectral technology. Effects of pH value, NaCl concentration, nanogold concentration, aptamer concentration, and the reactation temperature and time on the resonance scattering intensity were considered in detail. The influence of coexistent substances on the determination of K+ was investigated, result showed that the common heavy metal ions such as Cu2+, Mg2+, Pb2+, Ca2+, Al3+, Zn2+ and Fe3+do not interfere with the determination, and the method has good selectivity. Under the conditions selected, a 0.67-3 350 μmol·L-1 K+ can be detected by the aptamer-nanogold RS assay, with a detection limit of 0.3 μmol·L-1 K+, regression equation ΔI=0.167c－0.7, and a coefficient of 0.993 2. The method was used for analysis of K+ in serum sample with the results consistent with the ion-selective electrode method.