Reduction of water resources and renewable per capita in last 30 years is put Iran on crisis threshold. Therefore, in recent decades, wastewater as new resource for using in various fields has been placed on the agenda.Wastewater reuse is one of the battle solutionsfor loss water and prevents wastewater depletion and environmental pollution. Sewages generated from industrial activities can contain pollutants and if left untreated, can cause serious harm to the environment. Biological treatments are important methods for wastewater treatment that treats wastewater from pollutants, and treated wastewater could reused as reliable alternative water source.Biological treatments by removal of COD, BOD, PO4, TN and TSS from wastewater make a reliable source of water for using in agricultural, industrial and no potable goals. Thus, a pilot scale experiment was carried out to evaluate an integrated anaerobic/aerobic treatment for removal of organic matter, P and N from wastewater, also to reduction of hydraulic retention time by considering optimum removal efficiency. The pilot was an up-flow anaerobic/aerobic bioreactor type under continuous-feeding regime based on a central composite design. Parameters were analyzed using response surface methodology. The pilot was studied in different retention timesand aeration was carried out between 5-15 hours. According to different retention time for COD removal efficiency, 24 hours was selected as optimum hydraulic retention time, that it is comparable to those obtained for 48 hours and over in plant roughly and could remove COD and BOD in an acceptable rangesThe results showed that the average removal efficiency for BOD 5 were63.86and 83.99 percent in aerobic and anaerobic phases, respectively. The average removal efficiency for COD was 76.5 and 74.35 percent for anaerobic and aerobic sections, respectively. the average removal efficiency for BOD 5 and COD in this integrated areobic-anaerobic pilot 95.24 and 94.8 percent, respectively. The removal efficiency of this treatment method for PO 4 was 62. 67% and the effluent PO 4 concentration was 13. 42 mg/L on average. Theaverage removal efficiency for TN and TSS were 51.35 and 92.21% respectively, and the effluent nitrate concentration was 25.54 mg/ on average.In conlusion, the results obtained from this study showed BOD 5 , COD, PO 4 , TN and TSSeffluent concentrations were under aloowed optimal levels and could reuse in agriculture or return to the environment, and confirmed the viability of an integrated anaerobic-aerobic system for industrial wastewater treatment. Key Words: BOD 5 , COD, TSS, PO 4 , TN, NO 3 , Hydraulic Retention Time, Anaerobic aerobic Biological Treatment.