This method is based on the catalytic effect of Mo(VI) on the redox reaction between ethyl orange and hydrazine sulfate in sulphuric acid medium at 100°C, and in 0.03 mol/L H2SO4- 0.30 mol/L NH3-H2O supporting electrolyte. Ethyl orange exhibits a sensitive polarographic wave at -0.52 Vvs.SCE and change of ethyl orange concentration is traced by a polarographic detection technique. The detection limit and the linear range of Mo(VI) are 3.54 ng/mL and 20 to 300 ng/mL respectively. This new catalytic method has been applied to the determination of molybdenum in food, with satisfactory results.