Effect of acidic pretreatment of arsenic-bearing gold concentrate, a promising gold source, on its chemical composition and efficiency of its bacterial oxidation (BO) was studied. The titer of sulfobacilli during BO of the concentrate after high-temperature acidic treatment was 9.0 x 10(7) cells/ml, the degree of arsenic sulfide oxidation being 71.1%, and in the control, 6.5 x 10(7) cells/ml with the oxidation degree as low as 48.7%. Deeper oxidation of the main gold-containing mineral, arsenic sulfide, would allow more efficient gold recovery from the concentrate.