Schwertmannite has been proved to be a novel material which acts as a specific adsorbent for removing heavy metals or metalloid in contaminated water. Biogenic schwertmannite has received much attention in recent years due to its relatively strong adsorption capacity. In this study, the effect of initial Fe(Ⅱ) concentration on the formation of biogenic schwertmannite was investigated through the oxidation of FeSO₄ by Acidithiobacillus ferrooxidans. The results showed that the relationship between the initial Fe(Ⅱ) concentration (x, mmol/L) and the resulting mineral weight (y) could be expressed as y(g)=0.036 67+0.008 520x-8.602·10^-6x², or the relationship between initial Fe(Ⅱ) (x, mmol/L) and total iron removal efficiency (y) could be described by the equation y(%)=39.68-0.221 0x+ 6.653·10^-4x² when the concentration of Fe(Ⅱ) in the form of FeSO₄·7H₂O was 20～160 mmol/L, and the bacterial density was approximately 6.0×10⁷ cells/mL in 250 mL solutions. In the process of the reaction, lots of residual Fe³⁺ remained not precipitated although the saturation index is larger than 0. It is presumed that schwertmannite formation resulting from Fe³⁺ hydrolysis was probably caused by the energy obtained through the oxidation of Fe²⁺ by Acidithiobacillus ferrooxidans, which was supported by the fact that the generation of biogenic schwertmannite did not increase any longer after Fe²⁺ in solution was thoroughly oxidized by A. ferrooxidan, although a plenty of Fe³⁺ still existed in the reaction solution.