Background: A new biological domestic wastewater treatment process, which has been presented these days in activated SLUDGE modification, is Upflow SLUDGE Blanket Filtration (USBF). This process is aerobic and acts by using a SLUDGE blanket in the separator of sedimentation tank. All biological flocks and suspended solids, which are presented in the aeration basin, pas through this blanket. The performance of a single stage USBF process for treatment of domestic wastewater was studied in laboratory scale.Methods: The pilot of USBF has been made from fiberglass and the main electromechanical equipments consisted of an air compressor, a mixing device and two pumps for SLUDGE return and wastewater injection. The wastewater samples used for the experiments were prepared synthetically to have qualitative characteristics similar to a typical domestic wastewater (COD= 277 mg/l, BOD5= 250 mg/l and TSS= 1 mg/l).Results: On the average, the treatment system was capable to remove 82.2% of the BOD5 and 85.7% of COD n 6 h hydraulic retention time (HRT). At 2 h HRT BOD and COD removal efficiencies dramatically reduced to 50% and 46.5%, respectively.Conclusion: Even by increasing the concentrations of pollutants to as high as 50%, the removal rates of all pollutants were remained similar to the HRT of 6 h.