Abstract: With the development of papermaking industry, the demand for fresh water and discharge of wastewater become a severe problem. In this work, a membrane bio-reactor(MBR) was employed to treat papermaking wastewater, and the effects of membrane pore size and operation parameters on the performance of MBR were investigated. In addition, membrane filtration behavior and fouling phenomena were analyzed. The optimized membrane pore size is found as 300 nm with aeration rate of 1800 L·(m²·h)^-1, membrane flux of 19 L·(m²·h)^-1 and mixed liquid suspended solids(MLSS) of 6 g·L^-1. During a long-term run of 105 days, membrane performance keeps stable and the increase of atmosphere temperature prolongs the operation cycle. Meanwhile, the effluent quality is superior to that of traditional processes. The average removal rate of COD, turbidity, NH₃-N, TP, chromaticity and TOC are 92%, 99%, 93%, 73%, 98% and 88%, respectively. The analysis results show that organic matters are the main factors causing membrane fouling when MBR is used. However, the high content of Ca(9%) indicates that inorganic fouling should also not be neglected in papermaking wastewater. When the transmembrane pressure(TMP) reaches to 40 kPa, the fouled membrane is immersed in NaClO(0.5%(wt)) and then citric acid(0.3%(wt)) solutions for 2 h, respectively the membrane flux can be recovered up to 92% of its original value.