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Background and Aims: Bioremediation of soils contaminated with metal(loid)s is an attractive research area due to its sustainability and economic benefits. In the Slovak Republic, there are several abandoned mines containing high concentrations of arsenic (As) and antimony (Sb). This calls for new options for removing these hazardous metalloids from contaminated substrates. Studies on bioleaching of soils co-contaminated with both metalloids are very rare. This study aimed to test the effectiveness of bioleaching of soils heavily co-contaminated with As and Sb (up to 1463 mg.kg–1 and 5825 mg.kg–1, respectively) at a former stibnite mining site (Poproč, eastern Slovakia) through biostimulation and bioaugmentation. Methods: Bioleaching of As and Sb from four soils was induced by biostimulation of autochthonous microflora with Sabouraud medium (SAB) and SAB+glucose, and bioaugmentation of the soil with bacterial strains Cupriavidus oxalaticus and Cupriavidus metallidurans. Soil samples were subjected to determination of physico-chemical properties, microbiological parameters, and additional mineralogical analysis. Results: An inverse relationship between the total metalloid concentration and the microbial diversity was confirmed. In experiments with Cupriavidus metallidurans and Cupriavidus oxalaticus, mean bioleached As fractions were 37.6% and 41.3%, while Sb bioleaching was significantly lower, ranging between 17.0–26.2%. The mean bioleached fraction of As and Sb using SAB was 40.7% and 14.4%, respectively. The addition of glucose to SAB increased As bioleaching (50.7%) but not that of Sb. Conclusion: Collectively, the results highlighted a role of microorganisms in the mobility of metalloids in soils with their prospective applications in remediation of contaminated sites. [ABSTRACT FROM AUTHOR]