[en] U(VI) dissolved in a modified lactate-C medium (either sulfate- or lactate-limited) was reacted with a mixture of an Fe(III)-(hydr)oxide mineral (hematite, goethite, or ferrihydrite) and quartz under anoxic conditions and equivalent mineral surface areas. After sorption equilibration, the suspensions were inoculated with a sulfate-reducing bacterium (SRB, Desulfovibrio desulfuricans G20). Inoculation of the suspensions containing sulfate-limited medium yielded significant SRB growth, along with concomitant reduction of sulfate and removal of U(VI) from solution. Inoculation of the suspensions containing lactate-limited medium yielded similar results while lactate was still present. Once the lactate was depleted, however, some of the U that had been removed from solution was re-solubilized in the hematite treatment and, to a lesser extent, in the goethite treatment. No re-solubilization was observed in the lactate-limited ferrihydrite treatment even after a prolonged incubation of four months. Analysis by U L3-edge XANES spectroscopy of mineral specimens sampled without inoculation yielded a typical U(VI) spectrum. Mineral specimens sampled at the end of the experiment yielded spectra similar to that of uraninite, thus providing strong evidence for SRB-promoted removal of U(VI) from solution by reductive precipitation of uraninite. Consequently, U re-solubilization was attributed to re-oxidation of the uraninite by Fe(III) present in the (hydr)oxide phases. Our results thus suggest that inoculation with SRB mediates reduction of soluble U(VI) to an insoluble U(IV) oxide so long as a suitable electron donor is available. Depletion of the electron donor may result in partial re-oxidation of the U(IV) to soluble U(VI) species when the surfaces of crystalline Fe(III) (hydr)oxides are incompletely reduced by reaction with SRB-generated sulfide