The nanometer-sized materials have attracted much interest of analysts in recent years because of their special physicschemistry characteristics. As the scale decreases to nanometer grade, the number of atoms on the surface increases remarkably, resulting in the unsaturation. This makes the nanometer-sized materials have a high adsorptivity for the metal atoms. In the present paper, the nanometer-sized TiO2 was applied in the separation and preconcentration of Cr(III) and Cr(VI) in water. The influence of pH on the adsorption of Cr(III) and Cr(VI) was studied. When pH is larger than 6, 90%, Cr(III) is adsorbed onto the nanometer-sized material surface, while is basically not adsorbed in aqueous solution. Therefore, the separation of Cr(III) and Cr(VI) is achieved. At the pH of 6.5, Cr(III) was adsorbed by nanometer-sized TiO2 and desorbed with 2.0 mol x L(-1) HCl, in which the Cr(III) could be preconcentrated. The Cr(III) solution, as well as the Cr(VI) aqueous solution was determined by FAAS. The detection limits of Cr(M) and Cr(VI) were 41 and 57 ng x mL(-1), respectively. And the linear ranges for Cr(III) and Cr(VI) were 0-9.0 microg x mL(-1) and 0.1-10 microg x mL(-1) with a RSDs of 2.6% and 3.4% (n=6, c = 2.0 microg x mL(-1), respectively. This method was applied in the simultaneous determination of Cr(III) and Cr(VI) in the industrial wastewater and river water, and the satisfactory recovery results were obtained.