Membrane fouling is a critical problem for efficient commercialization of nanofiltration plants. A nano-MgO/GAC (Granular Activated Carbon) process was investigated the feasibility of using as pre-treatment for nanofiltration. Based on the results obtained, nano-MgO could decrease 51% of Permanganate Index (COD(Mn)), 60% of the ultraviolet absorbance at 254 nm (UVA(254)), and more than 99% of colony counts within 6 h. The pH increased to about 10.30 within only 0.5 h and then kept stable in the system containing nano-MgO. In addition, adding GAC led to less organic matters (remaining 4.74 mg.L(-1) versus 6.80 mg.L(-1)) and bacteria (13 CFU.mL(-1) versus 15 CFU.mL(-1)) relative to using nano-MgO only. Furthermore, almost all nano-MgO could be adsorbed by the GAC column. The pH value of the effluents from the nano-Mg and GAC was 10.18 and 10.20, respectively, while that of the effluent after KH(2)PO(4) adjustment could keep about 7.10. (C) 2011 Elsevier B.V. All rights reserved.