Natrojarosite is a very important material. In this paper biosynthesis of pure natrojarosite by immobilized Acidithiobacillus ferrooxidans was described. Scanning electron microscopy (SEM), ICP-AES and XRD analysis revealed the character of natrojarosite. The process is principally influenced by extracellular substances. H+ reduction and the oxidation of Fe2+ can accelerate production of the precipitation. Monovalent cation of the precipitation depends on pH value, especially the type and concentration of monovalent cation in solution. This research thus shows a novel application of A. ferrooxidans. (C) 2013 Elsevier B.V. All rights reserved.