Quorum sensing (QS) is a microorganism communication system. This study verified the potential existence of the QS system among ANaerobic AMMonium OXidation (anammox) bacteria. The release of three Acyl Homoserine Lactones (AHLs; C-6-HSL, C-8-HSL, C-12-HSL) by anammox culture was confirmed. By conducting series of batch test, the introduction of exogenous C-6-HSL and C-8-HSL could significantly increase activity of anammox bacteria, and meanwhile, C-6-HSL significant increased the growth rate, finally resulting in the increased ammonium nitrogen removal performance of 35% and 20%, respectively, whereas the exogenous C-12-HSL apparently promoted the growth of heterotrophic bacteria in the community. To further identify how exogenous signal molecular affects anammox culture, analyses of anammox culture supernatant and biomass extraction revealed that these additional signal molecules activated bacteria by inducing the production of endogenous signal molecular by anammox culture. This study might open a new window to overcome the disadvantage of the long-start-up period of anammox reactor restricting the development of current anammox process. (C) 2015 Elsevier B.V. All rights reserved.