A pilot-scale(10 m3/d) anoxic/oxic membrane bioreactor(A/O MBR) was tested for dyeing wastewater treatment of woolen millwithout wasting sludge in 125 days operation. Results showed that the effluent quality was excellent, i.e. effluent COD less than 25 mg/L,BOD5 under 5 mg/L, turbidity lower than 0.65 NTU, and colour less than 30 DT, and met with the reuse water standard of Cb. ina. The removalrates of COD, BOD5, colour, and turbidity were 92.4%, 98.4%, 74% and 98.9%, respectively. Constant-flux operation mode was carriedout in this study, and backwash was effective for reducing membrane fouling and maintaining constant flux. Membrane fouling had heavy impacton energy consumption. More attention should be paid on pipe selection and design for the sidestream MBR system, too.