The oxidation of ferrous sulfate by Thiobacillus ferrooxidans(ATCC 19859) and iron-oxidizing microorganism of the isloate from the night soil treatment plant was studied for the basal experiment of biological leaching using fluidized bed reactor. They are the most important microorganism in acid mine drainage, a serious environmental problem. From the experimental results of ferrous sulfate oxidation the optimum conditons of FeSO4 oxidizing was observed at the inoculated cell concentration 30%(v/v), 30 ℃ of medium temperature, pH 2.0, 1.0vvm and 200mM FeSO4, respectively. The pH drop in medium indicated that ferric iron is hydrolysis in aqueous solution. In the presence of Thiobacillus ferrooxidans 90% of 160mM ferrous sulfate within 2days and iron-oxidizing microorganism 85% could be leached out from the 400mL of fluidized bed reactor.