A three-stage sequencing batch reactor (SBR), comprising pretreating SBR (SBRpre), nitritation SBR (SBRni), and anaerobic ammonium oxidation (Anammox) SBR (SBRana), was developed for the nitrogen removal from mature landfill leachate. The concentrations of ammonia and chemical oxygen demand (COD) in the leachate were 2000 +/- 100 and 2200 +/- 200 mg/L, respectively. About 100 mg/L of organic substance was removed from SBRpre to reduce the negative effect on the Anammox process under real-time control. After acclimation for 40 days, the nitrite to nitrogen oxide ratio (NO2-/NOx) in SBRni was above 0.95. The nitrogen removal efficiency reached 90% in SBRana, and nitrogen load rate and nitrogen removal rate were 0.81 and 0.76 kg N/(m(3) d), respectively. The continuous filling process was used to avoid the nitrite inhibition on the Anammox activity. The quantitative PCR analysis of Anammox indicated the average Anammox gene ratio increased from 0.23% to 4.77% after 220 days operation. (C) 2014 Elsevier Ltd. All rights reserved.