An integrated Bioreactor (IB) with three compartments (Aerobic, Anoxic and Clarifier) of total volume 180 L was successfully employed for the removal of Chemical Oxygen Demand (COD) from a simulated synthetic domestic wastewater at 25±2°C. Chemical Oxygen Demand (COD) (250-500 mg L-1) and hydraulic retention time (HRT 12 and 7.2 days) were varied. The bioreactor was inoculated with MLSS concentration of 3000 mg L-1. Results show that with initial COD concentration of 500 mg L-1, COD concentration decreased to 92-80 mg L-1 in the aerobic compartment and 81-71 mg L-1 in the anoxic compartment when HRT was raised from 7.2-12 days. COD concentration in the effluent was 74 and 44 mg L-1 at HRT of 7.2 and 12 days, respectively. Increased in organic loading did not show any significant effect in the aerobic compartment (83.4 and 84) at 250 and 500 mg L-1 COD concentration, respectively. However, COD removal decreased in the anoxic compartment (90 and 86) and the net effluent (95 and 91) at 250 and 500 mg L-1 initial COD concentration. The substrate utilization rate was higher for the aerobic compartment (1.1919 day-1 m3 kg-1) but lower for the anoxic compartment (0.1725 day-1 m3 kg-1). Growth of microbial population was most significant in the aerobic compartment. Ammonia and nitrate was monitored and a removal of 94 and 83 was achieved respectively, at steady state. The obtained results demonstrate that an IB can be applied in the removal of medium strength COD from wastewater. © 2015 Asian Network for Scientific Information.