Sulfonated multiwall carbon nanotube (SMWCNT) with pendant alkyl sulfonic acid groups was synthesized from hydroxyl-functionalized multiwall carbon nanotube (MWCNT-OH). Small changes in microstructure, due to nucleophilic substitution reaction, were confirmed by X-ray photoelectron spectroscopy, transmission electron microscopy, and N-2 adsorption-desorption measurements. Prepared SMWCNT exhibited excellent water dispersity, which facilitated interfacial polymerization to prepare novel poly(piperazine amide) thin-film nanocomposite (TFN) membranes. Water flux and salt rejections of the TFN membranes were readily adjusted by optimizing the SMWCNT content, to get most optimum separation performance. TFN-0.01% showed high water flux of 13.2 L m(-2) h(-1) bar(-1), 1.6 times more than the pristine thin-film composite (TFC) membrane, maintaining reasonably high rejection of 96.8% to Na2SO4. TFN-0.01% membrane, with enhanced surface hydrophilicity exhibited better anti-fouling ability to bovine serum albumin with water flux recovery ratio as high as 91.2%, even after two "fouling-washing" cycles, compared to 82.0% for TFC membrane.