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 tech- niques were examined, and the relative importance of polysac- charides 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 sedi- mentation, 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 re- moved throughout the treatment process. Special attention was paid to the differences in fouling potential of different polysac- charides 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).