Abstract: In China surface water pollution has made quality drinking water production difficult. The major pollutants in surface water are organic matter measured by COD_Mn and ammonia nitrogen. To remove these pollutants effectively, membrane bioreactor (MBR) was studied as a substitute for the conventional water treatment process. Powdered activated carbon (PAC) was dosed into the reactor to enhance the treatment efficiency. A pilot scale MBR was operated continuously for 130 days. In this period, 79.1% of COD_Mn, 85.9% of UV₂₅₄, 97.9% of UV₄₁₀, 99.6% of turbidity and 97.4% of NH₃-N could be removed, and the total coli-group was not detectable per 100 ml in the treated water. Concerning the accumulation of refractory organics in the reactor, an index A_m(organics accumulative factor in the mixed liquor) was proposed. It helps to evaluate the efficiency of biodegradation and PAC adsorption of organic pollutants in the reactor. Moreover,A_m appeared to have a negative effect on the removal efficiency of organic pollutants.At the end of the pilot test, three-step cleanings were carried out for the fouled membrane. The flux recovery for each cleaning step was measured, and the composition of the eluted foulants after each chemical cleaning step was analyzed. The results demonstrated that organic pollutants were the major membrane-fouling substances, and chemical cleaning with 0.4% sodium hypochlorite could remove them efficiently.