Domestic wastewater was treated by combined anaerobic biofilm-aerobic membrane(MBR) process, and part biomass in MBR was withdrawn to treat with ozone, then the ozonated sludge was returned to anaerobic inlet. In aerobic MBR, MLSS and DO were controlled at 3000-3500 mg/L and 0.8 mg/L respectively, compared the experimental results of two stages, it was noticed that ozonation did not affect the removal efficiency for organics but had a significant influence on the removals of NH3-N and TN. During the ozonation period of two months, no excess sludge was wasted, and a zero sludge yield was obtained.