It was found that there were some kinds of sulfur-oxidizing bacteria in the acidic mine water, and these bacteria could promote the dissolution behavior of heavy metals in the mining smelting waste slags. In this paper we collected a bacterium sample form a mining-water of an abandoned pyrite mine in the southwest of China and named it as FJ strain. We isolated and purified the FJ strain by 9K medium, and then made a primary identification of the purified strain. The FJ strain was gram-negative and in the shape of short rod. The strain was chemoautotrophic and aerobic bacterium, and it could oxidize the ferrous ion or the reduced sulfur as energy source to main the metabolism. The optimum growth temperature and pH is 30 °C and 2.0 separately. And we also found the strain had a considerable acid-producing ability and was eosinophilic. After a comparison and analysis, we confirmed that the physiological and biochemical characteristics of the isolated FJ strains were consistent with that of thiobacillus ferrooxidans, T ferroxidans for short. Therefore we drew a conclusion that the FJ strain we purified was just the target strains T ferrooxidans, the isolation-purification of the bacterium sample was successive.