Abstract: The characteristics of submerged membrane bioreactors (SMBR) with and without powdered activated carbon (PAC) addition were investigated respectively under identical feed and operation conditions. A series of experiments were conducted on both systems to analyze filterability, floc in the bulk solution and the effect of PAC contents on hydraulic resistance. The results demonstrated that pronounced flux enhancement was achieved by PAC addition. The different filtration performance between the two systems might mainly stem from the different characteristics of bulk phase. With the increase of PAC content, the decrease rate of hydraulic resistance will be reduced. Investigation of the reactors stability to organic shock loads showed that BPAC-SMBR has better buffer capacity than AS-SMBR.