The effectiveness of ozonation was investigated in the aspect of in situ control of the membrane fouling in drinking water treatment. A compacted system with a scale of 120 m(3)/d was built by integrating coagulation, ozonation and ceramic membrane into one tank. A flat-sheet ceramic membrane with a pore size of 60 nm was selected. The quantity of foulants was measured in terms of total organic carbon and dissolved organic carbon (DOC). The properties of organic fouling were characterized with hydrophobicity and specific ultraviolet absorbance. The results showed that membrane fouling was alleviated through in situ ozonation with ozone dosages of 2.0 similar to 2.5 mg/L; the membrane working cycle time could be doubled under the tested conditions. However, the membrane fouling accumulated gradually with DOC as the major foulants. The in situ zonation may have transformed organic molecules into smaller ones and derived more carboxylic groups, thus made them to be more hydrophilic during the oxidation process. It was concluded that zonation had happened inside the membrane pores, leading to the change of the molecular structures of the organics. It is believed that in situ ozonation is of substantial significance in the improvement of ultrafiltration for drinking water treatment. (C) 2013 Elsevier B.V. All rights reserved.