In　this　study,　laboratory-scale　experiments　were　conducted　by　using　Sequencing　Batch　Reactor　(SBR)　activated　sludge　process　to　treat　wastewater　stream　from　a　pharmaceutical　factory.　Biological　nitrogen　removal　can　be　achieved　via　partial　nitrification　and　denitrification　and　its　efficiency　was　above　99%　at　23℃±1℃.　The　experimental　results　indicated　that　the　nitrite　oxidizers　were　more　sensitive　than　ammonia　oxidizers　to　the　free　ammonia　in　wastewater.　The　ammonia　was　oxidized　at　pH　7　and　7.5　respectively,　which　suggested　a　critical　free　ammonia　concentration　of　0.2mg*L-1　at　which　the　nitrite　oxidizers　were　inhibited.