The objective of this study was to evaluate the characteristics of colloidal natural organic matter (NOM) in terms of biodegradability, organic fouling and/or biofouling of the membrane. From the FTIR spectral analyses of colloidal NOM, they have been found to contain a high BDOC content (38%), including the N-acetyl groups of amino sugars and polysaccharides. The effects of size and charge of NOM fractions were considered. Heterotrophic bacteria can be attached and taken in despite their large molecular size. Bacteria can also move toward their favorite organic compounds with negative charge. Due to these characteristics of colloidal NOM their effects in drinking water treatment processes can be reduced by biological pre-treatment processes. Colloidal NOM exhibit a significant flux decline compared to other NOM constituents, such as hydrophobic and bulk NOM. Includes 5 references, tables, figures.