To　investigate　the　physiological　and　ecological　characteristics　of　methangens　in　the　steady-state　of　anaerobic　baffled　reactor　(ABR),　a　laboratory-scale　ABR　with　seven　compartments　was　operated　with　molasses　wastewater　as　substrate.　Chemical　analyses　were　done　to　evaluate　digester　performance.　In　parallel,　Archael　community　dynamics　were　monitored　by　single　strand　conformation　polymorphism　(SSCP)　analysis　targeting　the　V3V5　region　of　16S　rRNA　genes　and　further　characterized　by　partial　sequencing　of　16S　rRNA　genes.　The　result　showed　obviously　niche　separation　between　the　acidogenic　phase　(1st　to　4th　compartments)　and　the　methanogenic　phase　(5th　to　7th　compartments).　The　acidogenic　phase　obtained　richer　diversity　and　the　dominant　genus　up　to　15　OTUs,　among　which,　Methanobacterium　and　Methanosarcina　were　dominant　genera.　At　the　same　time,　in　the　methanogenic　phase,　the　dominant　status　of　Methanobacterium　was　replaced　by　Methano-genium　and　some　new　Methanosarcina　sp.　that　can　utilize　acetate　as　substrate,　and　the　dominant　genus　reduced　to　8　OTUs.　95%　sequenced　bands　belong　to　three　genera,　i.e.,　Methanobacterium,　53%;　Methanosarcina,　24%;　Methanogenium,　18%.　©　2009　IEEE.