In　order　to　study　the　influences　of　organic　carbon　source　on　the　microbial　community　structure　in　partial　nitrification　system,　the　microbial　diversity　was　investigated　in　two　partial　nitrification　reactors　by　the　construction　of　bacterial　clone　library.　The　influents　of　two　reactors　were　artificial　wastewater　with　and　without　organic　carbon　source,　respectively.　The　results　indicated　that　Proteobacteria　and　uncultured　bacterium　were　the　dominant　bacteria　of　the　two　studied　systems.　The　differences　existed　in　the　structure　of　the　bacterial　community　of　the　two　systems.　Nonetheless,　the　dominant　bacteria　and　their　proportions　were　similar　to　each　other　in　the　total　clones.　In　addition,　the　main　denitrifer　groups　were　also　similar　in　the　two　systems.　Due　to　the　different　concentrations　of　organic　carbon　source,　the　denitrifer　genera　and　their　proportions　were　distinct.　The　main　denitrifer　genera　of　partial　nitrification　reactor　with　inorganic　wastewater　were　Nitrosomonas,　Nitrospira　and　Denitratisoma.　The　proportion　of　autotrophic　nitrifying　bacteria　in　partial　nitrification　reactor　with　inorganic　wastewater　was　higher　than　that　with　organic　wastewater.　But　in　the　reactor　with　inorganic　wastewater,　the　proportion　of　autotrophic　bacteria　was　lower　than　heterotrophic　bacteria.　The　main　denitrifer　genera　of　partial　nitrification　reactor　with　organic　wastewater　were　some　denitrifying　bacteria　of　β-Proteobacteria　and　Nitrosomonas.　Additionally,　the　proportion　of　the　latter　in　this　reactor　was　relatively　low.　©　2016,　Chinese　Society　for　Environmental　Sciences.　All　right　reserved.