The purpose of this work is to investigate an advanced water treatment system changes on disinfects by-products (DBPs) precursors removal efficiencies of treatment plant and associated trihalomethanes (THMs) and haloacetic acids (HAA(5)) formation and assimilable organic carbon (AOC) in reduction from raw water through finished water of Fong-shan Water Treatment Plant (FSWTP) in Kaohsiung City, Taiwan. Drinking water samples were collected from an advanced water treatment plant during March-October 2008. In the formation of DBPs, advanced water treatment processes efficiently removed THMs and HAA(5). The concentrations of THMs and HAA(5) in finished water were reduced to 13.97 microg/L and 17.67 microg/L, respectively. In this investigation, the AOC was reduced effectively by ozonation and biological activated carbon (BAC) processes. Experimental results of this 6-month investigation indicate that AOC concentrations in the finished water can meet the WTP criterion of 50 microg acetate-C/L in the world. Results of this study provide a valuable reference for solving DBPs and AOC control of water treatment plants and the setting of regulations in Taiwan.