Membrane fouling in a lab-scale anoxic-oxic MBR operated at low dissolved oxygen (DO) was investigated in this study. The system includes an anoxic, an oxic and a membrane basin with the working volumes of 73 L, 124 L, and 68 L, respectively. A hollow fibre membrane module with a pore size of 0.2 µm and with total filter area of 1.44 m2 was submerged in the membrane basin. The system was operated at various low DO concentrations of 2.0; 1.5; 1.0; and 0.5 mg/L. The results shown that at DO

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... than 1.0 mg/L, COD and TN removal efficiencies were higher than 90 % and 60 %, respectively. However, low DO (less than 1.0 mg/L) lead to poor sludge flocculation which deteriorate the membrane filterability. The TMP increased dramatically at different DO levels. There was a significant increase of TMP during first 15-days experiment at DO 2.0 mg/L. After that the TMP was increased slowly and lower than 16 kPa to until 30-days. In contrast, when DO was reduced to 1.5, 1.0, and 0.5, the TMP was increased sharply almost from 1 to over 20 kPa within about 15 days.