Three identical SBR adapted to different salinity were applied to investigate the characteristics of the treatment performance and N2O production (P-N2O) during shortcut biological nitrogen removal from landfill leachate under various operating parameters. Increase of salinity might deteriorate the activity of the microorganisms leading to the increase of P-N2O, however, the system could be gradually adapted to the inhibition and alleviate the detrimental effect to some extent. The system acclimated to high salinity provided better performance under high salinity shock and a lower possibility of P-N2O, while a sudden decrease in salinity can cause a temporary increase in P-N2O. High salinity strengthened the influence of high ammonia nitrogen concentration and low DO concentration on P-N2O while the strengthening effect was unconspicuous at high DO concentration. The anoxic phase did not produce a significant amount of N2O even at the lowest C/N ratio of 0.5 and was less susceptible to salinity. Characterization of the biomass composition using fluorescence in situ hybridization analysis confirmed that the relative proportion of Nitrosomonas europaea was increased with the increase of the salinity, which may be an important factor for the strengthening effect of salinity on P-N2O. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.