Abstract: Horseradish peroxidase(HRP)was immobilized by crosslinkage on the glassycarbon electrode to prepare the enzyme electrede ,where the reduction of H_2O_2 was studied in l,4-dioxane media. It was shown that HRP electrode can catalyze the reduction of H_2O_2 without anymedintor,however, as an activator,o-phenylenediamine can promote the bio-catalysis. In thepresence of the activator,the parallel reactions occurred on the enzyme electrode. The workingcondition of the HRP electrede was investigated as the sensors for H_2O_2 and o-phenylenediamine,alsothe influence of water content in organic phase was discussed on the performance of the enzymeelectrode in organic phase.