Natural Organic Matter (N0M) was isolated and extracted from a moderately-colored surface water, then fractionated using hydrophobic and ion exchangeresins into eight groups. Each was subjected to batch ozonation, and the rateof loss of ozone was measured. Then, selected fractions were analyzed forchanges in functional group content, molecular size and hydrophobicity; somewere further fractionated by size prior to functional group analysis. Fulvicacids and humic acids were the most reactive. These groups also showed thegreatest change in carboxyl group content and hydrophobicity. The results arediscussed with respect to impacts on coagulation. Although hydrophilicneutrals were of low to moderate reactivity, they showed the greatest promisefor improved coagulation following preozonation.