In recent years, there has been a growing interest in nanostructure membranes made of vertically aligned carbon nanotubes (VA-CNT) due to their potential of high water permeability. Nevertheless, membrane fouling is one of the most critical issues in these VA-CNT membranes. Accordingly, this study mainly focused on understanding of membrane fouling of VA-CNT membranes, which were prepared by thermal chemical vapor deposition (CVD) technique. Surface modification by graft-polymerization of methacrylic add (MA) was attempted to not only retard membrane fouling but also improve solute rejection. The resistance-in-series model was applied to characterize the properties of fouling layers. BSA (bovine serum albumin) was used as the model foulant Results indicated that the VA-CNT membranes had higher fouling propensity than polymeric membranes. After surface modification, however, irreversible fouling was significantly reduced in the VA-CNT membranes, which was attributed to an increase in hydrophilicity and surface charge. The rejection of BSA by VA-CNT membrane also increased after surface modification, suggesting that the surface charge played an important role in the rejection of charged molecules. (c) 2013 Published by Elsevier B.V.