Extracellular polymeric substances (EPS) extracted from iron bacteria can promote the iron aggregation and then form iron minerals by stabilization and deposition actions of ferric ions. In this paper, based on the key regulation or influence on ferric bio-mineralization by iron bacteria or their EPS, the authors introduced the bio-mineralization formation of iron oxyhydroxides in soluble EPS-containing solutions from Acidithiobacillus ferrooxidans cultures without/with Fe(Ⅱ) or Fe(Ⅲ) at various molar rates of Cl^-/SO₄^2-. It mainly described the change of solution pH values and the phases and structures of the formed iron minerals characterized by XRD, FTIR and FESEM. The decrease of solution pH values and the characterization results suggested that the micro-sphere schwertmannite covered by "pincushion" or nano-spheroid schwertmannite and micro-prism jarosite particles could form in all reaction solutions. The resulting iron precipitates uld be regulated by bacterial EPS, which, however, hardly had impact on ferrous oxidation, and addition of iron salts could promote the transformation of initial schwertmannite into jarosite phase. It was also demonstrated that phase transformation and particle agglomeration could be prevented with the increase of Cl^-/SO₄^2- molar ratios (i.e. increase of Cl^- content). This might be related to the higher SO₄^2- content occurring in the reaction solutions, which facilitated phase transformation of iron minerals and presence of the tightly assembled spheroid particle morphology.