The effect of salinity shock (5-60 g l(-1) NaCl) on anaerobic ammonium oxidation (Anammox) process performance was investigated. The response to the shock loads can be divided into three stages: a sensitive period, an interim stable period and a recovery period which lasted 6-26 d. When exposed to NaCl shocks for 12 h, the sludge retention time (SRT) of the reactor decreased with increasing NaCl shock loads, ranging between 2.9 and 22.5 d, meanwhile the biomass decreased by 0.8-37.4%. When shock loads were higher than 10 g l(-1) NaCl, the reactor was at risk of losing too much biomass. The granular surface was rough due to rapid growth of filamentous bacteria and extracellular polymeric substances (EPS), also the EPS amount changed during all NaCl shock loads. In the latter of shocks, the microorganisms in the reactor showed a little adaption to the NaCl shock. (C) 2012 Elsevier Ltd. All rights reserved.