Taking　the　mature　landfill　leachate　as　the　research　object,　the　nitrogen　removal　performance　of　the　ANAMMOX-UASB　(anaerobic　ammonia　oxidation　up-flow　anaerobic　sludge　blanket)　system,　the　ANAMMOX　granular　sludge　characteristics,　and　the　changes　of　its　size　distributions　were　investigated.　The　results　show　that　the　ANAMMOX-UASB　system　can　achieve　efficient　nitrogen　removal　in　mature　landfill　leachate.　At　the　stable　stage,　the　average　removal　rates　of　NH4+-N,　NO2--N　and　TN　were　96%,　95%　and　87%,　respectively.　The　activity　of　ANAMMOX　granular　sludge　was　very　well,　and　ANAMMOX　still　was　the　main　way　of　nitrogen　removal,　but　there　was　also　nitrogen　removal　by　heterotrophic　denitrification　simultaneously　in　the　system.　Moreover,　aerobic　ammonia　oxidation　and　nitrite　oxidation　existed　in　the　system,　and　their　activity　were　0.031　and　0.010　g/(g·d),　respectively.　The　color　of　granular　sludge　changed　from　brick　red　to　red-brown,　and　the　average　size　of　granular　sludge　changed　from　small　to　large.　At　the　stable　stage,　the　proportion　of　granular　sludge　size　exceeding　1.5　mm　was　81%.　There　were　spherical　bacteria,　rod-shaped　bacteria　and　filamentous　bacteria　on　the　granular　sludge　surface.　©　2016,　Editorial　Department　of　Journal　of　Southeast　University.　All　right　reserved.