A new method for the preparation of an organic-inorganic composite fihm of the heteropolyanion has been developed by modifying P(Mo2O7)6-7 to the indium tin oxide (ITO)electrode surface. The modified electrode displayed a strong catalytic activity towards the reduction of IO3-. In the range of 1.0×l0-6～5×l0-4mol/L, the catalytic current was linear proportional to the IO3- concentration.