Abstract: In a Clark-Lubs buffer medium of pH 7.0,a coordination complex was formed between Ni(Ⅱ) ion and 5-(5′-nitro-2′-pyridylazo)-2,4-dimethylamino toluene,and a sensitive adsorptive polarographic wave produced by this complex was observed with its peak potential (Ep) at -720 mV (vs.SCE).Linear relationship between the peak current (Ip) and the concentration of Ni was obtained in the range of 0.01-2.5 μg of Ni(Ⅱ) per liter of the solution,with a detection limit of 7.8 ng·L-1.It was proved by several electrochemical methods,that the polarographic wave is a complex-adsorptive wave,and the electrode process is a irreversible process,involving an electron-transfer number of 2.Interference tests of more than 20 anions and cations commonly co-existed were performed and selectivity of the proposed method evaluated.The method has been applied to the analysis of aluminum alloy.