Iron oxide-coated sand (IOCS) was modified with hexadecyltrimethyl ammonium (HDTMA) and tested as an adsorbent for the removal of natural organic matter (NOM) from water. The modification did not change the physical properties of the IOCS but coated HDTMA onto its surface. The HDTMA-modified IOCS displayed a faster initial NOM adsorption and substantially higher capacity than the unmodified IOCS over a wide pH range in both batch and column adsorption. The enhancement was more pronounced at higher pH. Compared to unmodified IOCS, the HDTMA-modified IOCS removed more hydrophobic and larger NOM molecules and its NOM adsorption was less sensitive to the changes in ionic strength. The adsorption capacity of the modified IOCS was regenerated in-situ with NaOH solution and ex-situ with HDTMA solution. HDTMA-modified IOCS adsorption may be a promising alternative technology for NOM removal. (C) 2009 Elsevier B.V. All rights reserved.