Sulfidogenic processes have been successfully used in saline wastewater treatment for sludge minimization, but are inapplicable in treating sulfate-deficit wastewater. This study reported a novel internal sulfur cycling (ISC) process for sulfate-deficit wastewater treatment. The process consisted of a sulfur-reducing reactor (SRR) for organics removal, followed by a sulfide-oxidizing reactor (SOR) and sedimentation tank for sulfur recovery. Under different hydraulic retention times and organic loading rates, the performance of ISC system was evaluated. The lab-scale ISC system removed 94% of chemical oxygen demand (COD), of which 81% were accomplished in the SRR by sulfur reducers without excessive sludge withdrawal throughout the 200 days of operation. The produced sulfide were mainly re-oxidized back to elemental sulfur in the SOR by sulfide-oxidizing bacteria, and sulfur balance demonstrates that 76% of sulfur recycling were achieved. Cost-benefit analysis reveals that the ISC process is a more cost-effective sludge-minimized biotechnology for sulfate-deficit wastewater treatment compared to conventional activated sludge processes.