The impact of a pre-treatment by pre-ozonation (2-10 mg O3/L) and subsequent coagulation (FeCl3: 2-6 mg Fe3+/L) on the performance of a polymeric ultrafiltration membrane was investigated in lab scale. The performance was assessed by monitoring the flux decline during filtration of secondary effluent in Amicon test cells. During the filtration process no free dissolved ozone was in contact with the membrane. It was observed that flux decline is reduced with increasing coagulant concentration as well as with increasing ozone dosage. This effect involves a reduction in the amount of biopolymers measured by size exclusion chromatography (LC-OCD). Moreover, multi-filtration cycles revealed that pre-ozonation leads to a significant increase in irreversible fouling that might be caused by increasing colloidal iron concentrations. Phosphorus in the permeate was successfully reduced to concentrations < 60 microg/L.