Recently there is an increasing interest in using all kinds of nanoparticles to construct electrochemical sensors,since they have high specific surface area,good biocompatibility,and good conductivity.Hydrazine is widely used as catalyst,corrosion inhibitor,reducing agent and pharmaceuticals.Therefore,the detection of trace hydrazine is very important in environmental and biological analysis.In this work a new modified electrode was prepared by electrodeposition of ruthenium nanoparticles (RNPs) at the surface of a bare glassy carbon electrode.Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values.The formal potential,E0′,of RNPs is pH dependent with a slope of -46.4 mV per unit of pH.The modified electrode was also employed to study electrocatalytic oxidation of hydrazine,using cyclic voltammetry,chronoamperometry,rotating disk voltammetry and amperometry as diagnostic techniques.The modified electrode exhibits potent and persistent electrocatalysis for hydrazine oxidation.The results show that in 0.1 M phosphate buffer solution (pH 7.0) the peak potential of hydrazine at the RNPs modified electrode is about 200 mV versuse Ag/AgCl,KCl (sat,d).The heterogeneous rate constant for electro-oxidation of hydrazine,k′,well determined using cyclic voltammetry and rotating disk electrode voltammetry.Amperometry exhibits a wide linear dynamic range and a good detection limit for hydrazine.Finally,the diffusion of coefficient of hydrazine was calculated as 3.3×10-6 cm2 s-1 for the experimental conditions,using chronoamperometric results.