The oxidation of arsenite (As^III) to arsenate (As^V) as an effective pre-treatment step was usually considered in order to ultimatly remove arsenic (As) from reducing aquatic environment such as groundwater. The present work selected quartz sand and pozzolan as two support materials filled into the parallel up-flow fixed-bed reactors. Concentrated As^III was completly oxidized with two support materials after inoculation of acclimatized arsenite-oxidzing bacteria (AsOB) with various HRT of 6 h, 3 h and 1 h. Moreover, pozzolan was more efficient than quartz sand for As^III oxidation even at a HRT of 40 min. Batch tests demonstrated that As^III oxidation rate was negatively correlated with the axial length of reactors, which was closely related with the AsOB distribution in the fixed-bed reactor. Finally, high efficient removal of As realized through the microbial As^III oxidation followed with the fixed-bed reactors filled with zero valent iron (ZVI) or negative ion-exhange resin.