Abstract: The start-up characteristics of membrane bioreactor(MBR) process(HRT: 0.5 h) with powdered activated carbon(PAC) as the support for bacterial growth was investigated for drinking water treatment.The results showed that when ammonia nitrogen was concerned,the natural start-up finished accomplished within 9 days after the initially difficult period(20 d).The MBR exhibited the stable removal of NH3-N with an average efficiency of 89.4% after the maturity of nitrosomonas group in the bioreactor.However,nitrite nitrogen was observed to accumulate in the MBR effluent during the maturation of nitrosomonas group and the start-up accomplishment lagged 6 days behind.While considering the organic pollutants removal,due to the synergistic effects of PAC adsorption and biodegradation,there was no clear indication for the maturity of heterotrophic bacteria. And the stable removal for organic matter was achieved by the MBR during the experiments.The average removal efficiency of TOC,COD_Mn,DOC and UV₂₅₄ were 26.4%,30.7%,20.4% and 21.7% on average,respectively.