When the pH values of solution were 6.5～7.5, the adsorption efficiency of nano-sized ZnO for As(Ⅲ) was higher than 99.5% in 10 min shaking. Based on the high adsorption capacity of As(Ⅲ) onto nano-sized ZnO and the good solubility of ZnO in acidic solution, a novel method for preconcentration of ultra-trace As(Ⅲ) by using ZnO was presented in the present work. After preconcentration and centrifugation, the supernatant fluid was removed. The sediment which contained the concentrated As(Ⅲ) was dissolved in HCl solution and the concentration was analyzed by hydride generation atomic fluorescence spectrometry (HGAFS). The proposed method possesses low detection limit (3σ) (0.075 μg·L-1) and good precision (the relative standard deviation (RSD) is 1.6%, n=6). The recovery rate for the analyzing of aquatic samples is between 97.0% and 104.5%. The results show that the method is simple, time saving and high sensitive.