The effects on sulfur removal and membrane fouling resulting from FeCl3 addition to an anaerobic fluidized membrane bioreactor (AFMBR) in a staged AFMBR (SAF-MBR) was investigated. Total sulfur removal in the SAF-MBR was 42–59% without FeCl3 addition, but increased to 87–95% with FeCl3 addition. Sulfide removal in the AFMBR increased to 90% with addition of FeCl3 at a molar Fe3+/S ratio of 0.54 and to 95% when the ratio was increased to 0.95. Effluent sulfide concentration then decreased to 0.3–0.6 mg/L. Phosphate removals were only 19 and 37% with the above added FeCl3 ratios, indicating that iron removed sulfide more readily than phosphate. Neither chemical oxygen demand nor biochemical oxygen demand removal efficiencies were affected by the addition of FeCl3. When the AFMBR permeate became exposed to air, light brown particles were formed from effluent Fe2+ oxidation to Fe3+. FeCl3 addition, while beneficial for sulfide removal, did increase the membrane fouling rate due to the deposition of inorganic precipitates in the membrane pores.