Oxidation of arsenopyrite with Acidithiobacillus ferrooxidans was studied.The electrochemical results show that arsenopyrite is firstly oxidized to As2S2 at the potential of 0.2-0.3 V (vs SHE) and As2S2 covers the electrode and retards the process continuously.While at higher potential over 0.3 V (vs SHE),As2S2 is oxidized to H3AsO3,and H3AsO3 is then oxidized to H3AsO4 at 0.8 V (vs SHE).The leaching results show that the addition of FeS2 can promote the oxidation of As3+ to As5+ and increase the activity of the bacteria.The best bio-oxidation technical parameters are the initial pH of 1.8-2.0,particle sizes less than 0.074 mm,temperature in the range of 25-30 ℃ and rotating speed of the orbital incubator of 100-160 r/min.The results provide theoretical and technological supports of bio-oxidation arsenopyrite for pretreating refractory arsenic gold ores.