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rejections of the membranes were both improved at the same time [22,24]. Shawky's results suggested that the addition of MWCNTs improved the rejection of both salt and organic matter for PA base FO membrane [25]. Zhang et al. introduced MWCNTs functionalized with isocyanate and 5-isocyanato-isophthaloyl chloride into PSF ultrafiltration membranes, and found that MWCNTs influenced surface mean pore size and porosity of membrane. As a result, with an appropriate amount of modified MWCNTs, the water flux of the membrane was enhanced [20].In this paper, to investigate the effect of MWCNTs on the structure and properties of FO membranes, MWCNTs were incorporated into the CDA matrix during the phase inversion process. The concentration of nano-tubes in the polymer matrix was controlled from 0 to 5wt% AbstractTo improve the performance of Cellulose di-acetate (CDA) based forward osmotic (FO) membrane in sea water desalination process, functionalized multi-walled carbon nano-tubes (MWCNTs) were blended as additives at varied compositions, from 0 to 5 wt%, into the solutions to prepare FO membranes using a classical phase-inversion method. The structure and property of the formed membranes were characterized by Fourier transfer infrared (FT-IR) spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Transitional Electron Microscopy (TEM), Water Flux and Reverse Solute Flux Tests. It was found that the content of functionalized MWCNTs was an important factor influencing the morphology, porous structures and properties of the blend membranes. SEM, AFM and TEM images of the blend membranes showed that the surface morphology and the cross-sectional morphology changed with the content of functionalized MWCNTs. It is interesting to see that at the presence of functionalized MWCNTs, the surface contact angle and the reverse solute flux of the FO membranes could be greatly improved without significantly affecting the pure water flux. With the addition of only about 1 wt% MWCNTs, the water flux of CDA based FO membrane was increased from 10.5 to 12.5 L/m 2 h while its reverse solute flux was reduced from 1.8 to below 0.3 mol/m 2 h. Desalination tests with 3.5 wt% simulated seawater feed solution had shown that the blend membrane with 1 wt% MWCNTs, was 366% higher in water flux and 53% lower in reverse solute flux than those of pure CDA FO membrane. These results suggest that CDA bases FO membranes modified with functionalized MWCNTs could possess good potential to be further developed for practical applications in the sea water desalination processes.