An arsenite (As[III])-oxidizing bacterium, SDB1, was isolated from mine tailing collected from the Sangdong mine area in Korea and showed chemolithotrophic growth on As[III] and $CO_2$ as the respective electron and carbon sources. SDB1 is Gram-negative, rod-shaped, and belongs to the Sinorhizobium-Ensifer branch of ${alpha}$-Proteobacteria. Growth and As[III] oxidation was enhanced significantly by the presence of yeast extract (0.005%) in minimal salt medium containing 5 mM As[III]; decreasing the doubling time from 9.8 to 2.1 h and increasing the As[III] oxidation rate from 0.014 to 0.349 pmol As[III] oxidized $cell^{-1};j^{-1}$. As[III] oxidation nearly stopped at pH around 4 and should be performed at pH 7~8 to be most effective. SDB1 was immobilized in calcium-alginate beads and the oxidation capaciti was investigated. Specific As[III] oxidation rates obtained with SDB1 (10.1~33.7 mM As[III] oxidized $g^{-1}$ dry cell $h^{-1}$ ) were 10~16-times higher than those reported previously with a heterotrophic bacterial strain (Simeonova et al., 2005). The stability and reusability of immobilized SDB1 strongly suggested that the immobilized SDB1 cell system can make the As[III] oxidation process technically and economically feasible in practical applications.