An advanced sewage treatment process has been developed, in which excess sludge reduction by ozonation and phosphorus recovery by crystallization process are incorporated to a conventional anaerobic/oxic (A/O) phosphorus removal process. The mathematical model was developed to describe the mass balance principal at a steady state of this process. Sludge ozonation experiments were carried out to investigate solubilization characteristics of sludge and change in microbial activity by using sludge cultured with feed of synthetic sewage under A/O process. Phosphorus was solubilized by ozonation as well as organics, and acid-hydrolyzable phosphorus (AHP) was the most part of solubilized phosphorus for phosphorus accumulating organisms (PAOs) containing sludge. At solubilization of 30%, around 70% of sludge was inactivated by ozonation. The results based on these studies indicated that the proposed process configuration has potential to reduce the excess sludge production as well as to recover phosphorus in usable forms. The system performance results show that this system is practical, in which 30% of solubilization degree was achieved by ozonation. In this study, 30% of solubilization was achieved at 30 mgO(3)/gSS of ozone consumption.