The heptadecatungstodiphosphate substituted by L a(Ⅲ) with the formula　α2-K7P2W17O61(La.OH2 ) (P2W 17La) was prepared by vacant refilling method. The anion of single substitu ted Dawson-type tungstophosphate salt was doped into the polypyrrole (PPY) film on a glassy carbon electrode (GC) by electrochemical method to prepare the chem ically modified electrode (P2W17La/PPY/GC). It maintains not only t he electrochemical activity and electrocatalytic property of P2W17L a, but also has good stability and sensitivity. In 0.50 mol/L HCl solution, th e first cathodic peak of P2W17La doping in polypyrrole film can cat alyze well the electroreduction of nitrite. The catalytic current was proporti onal to the concentration of nitrite between 6.0×10-5 and 1.0×10-2 　mol/L.