A　two-stage　UASB-A/O　system　was　introduced　to　treat　a　leachate　containing　high　organics　and　ammonia　from　an　immature　landfill　site.　The　simultaneous　denitrification　and　methanogenesis　were　successfully　carried　out　in　UASB1　and　the　effluent　COD　was　further　removed　in　UASB2.　The　biodegradation　of　residual　organic　substance　and　nitrification　took　place　in　the　A/O　reactor.　The　maximum　organic　removal　rates　in　UASB1　and　UASB2　were　12.5　and　8.5　kg/(m3　·　d),　respectively.　The　subsequent　nitrification　was　improved　significantly　due　to　the　lower　influent　COD　from　the　two-stage　UASB.　The　gas　production　rate　in　UASB1　was　0.28　m/kg　COD　at　30°C.　The　composition　of　biogas　CH4,　N2　and　CO2　was　relatively　constant,　accounting　for　63%-73%,　25%-35%,　and　about　2%,　respectively.　The　gas　production　rate　in　UASB2　was　0.40　mVkg　at　35°C　and　the　composition　of　boigas　CH4　and　CO2　was　also　relatively　constant　at　98%　and　2%,　respectively.　The　maximum　NH+4-N　removal　rate　was　0.68　kg/　(m　·　d)　and　NH-4-N　removal　efficiency　was　nearly　100%　by　complete　short-cut　nitrification　in　the　aerobic　reactor.　Biological　nitrogen　removal　for　leachate　with　high-strength　ammonia　was　realized　economically　and　effectively.