Elemental sulfur can serve as an economical external sulfur source replacing sulfate as an electron acceptor in sulfidogenic processes for wastewater treatment with sludge minimization. However, the biological sulfur reduction has not yet been considered in wastewater treatment due to the insolubility of sulfur. In this study, a laboratory-scale sulfur-reducing anaerobic fluidized bed (SRAFB) reactor was built to investigate the feasibility of the high-rate sulfur-reducing anaerobic wastewater treatment process. After 273 d of operation, the organics removal and sulfide production rates were determined as 1.71 kg CODc/m(3)-d (CODc: carbonaceous COD) and 2.71 kg S/m(3)-d, respectively, at a high organic loading rate of 2.14 kg CODc/m(3)-d with a hydraulic retention time of only 3 h. Biofilm growth on sulfur particles resulted in high sludge settleability (23 +/- 3 mL/g of SVI30) (SVI30: sludge volume index in 30 min) and thus high sludge concentration. As expected, a low sludge yield of 0.16 kg VSS/kg CODc (VSS: volatile suspended solids) was also obtained. Although sulfur reducers could not be identified in this study, Geobacter and Desulfomicrobium were the most likely sulfur reducers. This work suggests that elemental sulfur can serve as an electron acceptor in the new high-rate anaerobic sulfidogenic process for sludge-minimized wastewater treatment.