Anaerobic ammonium-oxidizing bacteria were successfully enriched in an upflow anaerobic sludge blanket bioreactor. In this balanceable ecosystem, the proportion between the conversion of ammonium and nitrite and the production of nitrate was found to be 1: 1.30: 0.29, and the removal efficiency of TN reached 90.35%. The microbial community and its diversity in enrichment cultures have been characterized using microscopy and molecular biotechnology. Based on 16S rRNA and phylogenetic analysis, we found four strains in the amplified DNA fragments. Three new species of anammox bacteria were found in this ecosystem.