This study was conducted to investigate the effects of powdered activated carbon (PAC) with immersed flat sheet membrane on the efficiencies of operation and treatment and to evaluate the performance of the system. The experiments were carried out under operating conditions of an average filtration rate of 0.65 m/d, water temperature of 22-26 degrees C, and PAC dose of 0 g/L (System A) and 20 g/L (System B). The regular influent concentrations of total organic carbon (TOC) and UV absorbance at 254 nm (UV254) were 3.186 mg/L and 1.7 l/m, respectively. TOC removal of 66.2 and 69.8%, and UV 254 removal of 70.6 and 82.4% were obtained from System A and System B, respectively. During an experimental period of 65 days, the value of TMP (trans-membrane pressure) in System B increased by 16 kPa, but the value of TMP in System B reached 61 kPa after 48 days. As a result, continuous filtration time was extended by using PAC. Bacteria count in the reactor of System B showed one hundred times higher than that of System A and most of the bacteria existed in the adsorbed state on the PAC. Higher biological activity can be expected by holding PAC in the filtration reactor. This study revealed that the filtrate quality and the performance efficiency were enhanced when PAC was introduced into the filtration system.