The effect of natural limonite on the growth of Acidithiobacillus ferrooxidans was studied through control experiments. The main phases of the natural limonite sample used in the experiments were identified as the mixture of goethite and hematite by X_ray diffraction analysis (XRD). UV_vis diffuse reflectance spectra and time_current curve under different irradiation conditions indicate that natural limonite has a good photoelectrochemical response. Dual_chambered system reactions were carried out with an “H"_type device. The results of three sets of control experiments show that A.f. grows better when external electrons are supplied by the photocatalysis of semiconductor minerals. Within 96 h, the cell density increases by 12 times. The variation of Fe2+ concentration is consistent with the growth curve of A.f. in control experiments, which reveals that natural limonite indirectly improves the growth of A.f. The mechanism can be interpreted as follows: Natural limonite can produce photo_generated electron_hole pairs under the visible light. The photo_generated hole is captured by the electron donor of ascorbic acid, while the separated photo_generated electrons transfer into cathode chamber to reduce Fe3+ to Fe2+. The process achieves the electrochemical regeneration of Fe2+, which provides adequate electron energy for the growth of A.f.