An　up-flow　oxygen-controlled　biofilm　reactor　filled　with　volcanic　filter　was　used　for　a　completely　autotrophic　nitrogen-removal　over　nitrite　(CANON)　process.　The　reactor　was　successfully　established　by　seeding　conventional　activated　sludge　at　ambient　temperature　without　additional　biomass　inoculation.　An　average　total　nitrogen　(TN)　removal　rate　of　1.1kg.(m(3)　d)(-1)　was　achieved　after　180　days＇　operation.　The　bacterial　morphology,　community　structure　and　spatial　distribution　of　nitrogen　removal　microorganisms　were　analyzed　by　using　some　molecular　biotechniques.　Denaturant　gel　gradient　electrophoresis　(DGGE)　profiles　showed　a　distinct　community　shift　of　nitrite　oxidizing　bacteria　(NOB)　during　the　start-up　period,　which　was　not　the　same　as　that　of　aerobic　ammonium-oxidizing　bacteria　(AerAOB)　or　anaerobic　ammonium-oxidizing　bacteria　(AnAOB).　Phylogenetic　results　indicated　the　predominance　of　Nitrosomonas,　＇Candidatus　Brocadia　fulgida＇　and　Nitrobacter　for　nitrogen　removal　in　the　system,　all　of　which　coexisted　without　a　distinguishable　niche　on　the　biofilm.