This study comparatively investigated ozonation and synthetic goethite-catalyzed ozonation of individual natural organic matter (NOM) fractions in terms of ozone consumption, dissolved organic carbon (DOC) and UV-absorbance reduction, molecular weight (MW) distribution, and formation of low-MW oxidation by-products. Hydrophobic acid and neutral (HOA and HON) and hydrophilic acid and base (HIA and HIB) were four major NOM fractions isolated from a filtered river water; so ozonation and catalytic ozonation were carried out on these fractions. Results indicate that in comparison to ozonation alone, catalytic ozonation can enhance ozone consumption, UV254 and DOC reduction, fragmentation of fraction components with MW > 3000 Da, and formation of oxalic acid for these fractions under normal reaction conditions commonly adopted in water treatment plants. in addition, catalytic ozonation can enhance aldehydes formation and increase the percentage of easy biodegradable organic carbon compared with ozonation alone for HIA and HIB, but exert much less effect on these items for HOA and HON. (c) 2007 Elsevier Ltd. All rights reserved.