In the study reported here, we investigated the combined fouling of UF membranes by NOM and inorganic particles found in natural water. The effects of various pretreatment techniques were examined, and the relative importance of polysaccharides and proteins in UF membrane fouling was evaluated. The water samples used as feed to the UF membrane were collected from a full-scale drinking water treatment plant (DWTP) at various stages in the treatment process. The full treatment process consisted of coagulation, followed by sedimentation, ozonation, up-flow BAC (UBAC) degradation, sand filtration, and chlorination (disinfection). The UBAC functioned more as a biological reactor than as a conventional down-flow BAC filter (Han et al., 2013). It was expected that both biopolymers and inorganic particles would be gradually removed throughout the treatment process. Special attention was paid to the differences in fouling potential of different polysaccharides in the feed water. A previous study showed that the polysaccharides could be roughly grouped into gelling and non-gelling components (Wang and Waite, 2009).