Multiwalled carbon nanotubes (CNTs) were thermally treated and were employed as adsorbents to study their characterizations and adsorption performance of natural organic matter (NOM) in aqueous solutions. The physiochemical properties of CNTs such as structure and nature of the carbon surface were changed after thermal treatment, which made CNTs adsorb more NOM. The amount of adsorbed NOM onto CNTs increased with a rise in initial NOM concentration and solution ionic strength but decreased with a rise in solution pH. A comparative analysis on the NOM adsorption between CNTs and granular activated carbon (GAC) was also conducted. Under the same conditions, the treated CNTs have the best NOM adsorption performance, followed by the raw CNTs and then the GAC, suggesting that the CNTs are efficient NOM adsorbents and possess good potential applications to maintain water of high quality. Further research works on testing the toxicity of CNTs and CNT-related nanomaterials are needed in order to promote safe and optimized applications of CNTs in water treatment. (c) 2007 Elsevier B.V. All rights reserved.