In this work, the electrochemical dissolution behavior of arsenopyrite in the presence of Sulfobacillus thermosulfidooxidans was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV results implied that the presence of S. thermosulfidooxidans could not affect the oxidation mechanism of arsenopyrite. The EIS diagrams showed different characteristics after different incubation times, indicating the change of arsenopyrite-solution interfacial processes during bioleaching. The arsenopyrite biooxidation was initially controlled by two electrochemical processes, involving arsenic and iron dissolution from arsenopyrite and the oxidation of elemental sulfur film on the arsenopyrite surface, and then the latter was replaced by the diffusion of oxidants (e.g., Fe3+ and O-2) or products (e.g., Fe2+). Additionally, high potentials could contribute to the promoted dissolution of arsenopyrite. Under potentials lower than 500 mV, the arsenopyrite oxidation was composed of two charge transfer processes, as described above. While the potential was higher than 500 mV, the arsenopyrite oxidation was changed into only one charge transfer process. This study would provide some valuable information for the pretreatment practice for refractory gold ores. (C) 2018 Elsevier Ltd. All rights reserved.