Nanometer barium-strontium titanate immobilized on silica gel G was successfully prepared by the citrate acid sol-gel method and characterized using X-ray diffraction (XRD),scanning electron microscope (SEM) and Fourier transform infrared spectrophotometer (FTIR).By means of the determination of flame atomic absorption spectrometry(FAAS),the adsorption behavior of immobilized nanometer-barium strontium titanate for cadmium ion was investigated.The results showed that the nanometer barium-strontium titanate was immobilized on the silica gel G firmly,gaining a new sort of adsorbent.And the cadmium ion studied could be quantitatively retained in the pH value range of 4-7.The adsorption behavior followed a Freundlich adsorption isotherm and a pseudo-second-order kinetic model.The thermodynamic constants of the adsorption process,such as enthalpy changes(ΔH),Gibbs free energy changes(ΔG) and entropy changes(ΔS),were evaluated.These showed that the adsorption of cadmium ion by immobilized nanometer barium-strontium titanate was endothermic and spontaneous physical process.The cadmium ion adsorbed could be completely eluted using 1 mol·L-1 HNO3.A new method for the determination of trace cadmium ion in water based on this immobilized nanometer barium-strontium titanate preconcentration and FAAS determination was proposed.The method has been applied to the determination of trace cadmium ion in tap water and river water with satisfactory results.