Partial　nitrification　(PN)　was　rapidly　started-up　in　a　sequencing　batch　membrane　bioreactor(MBR)　treating　domestic　wastewater　with　low　temperature　(11　similar　to　15　degrees　C),　the　influence　of　alkalinity　on　PN　process　and　the　feasibility　to　control　the　ratio　of　nitrite　to　ammonia　in　effluent　were　investigated　through　changing　the　ratio　of　Alkalinity/ammonia　in　influent.　Results　showed　that　effluent　ratio　can　be　controlled　flexibly　with　the　liner　relationship　between　ammonia　conversion　and　the　ratio　of　alkalinity　to　ammonia　when　alkalinity　is　insufficient,　whereas,　that　could　be　effectively　achieved　by　the　indicator　role　of　alkalinity　on　nitrite.　Phylogenetic　results　indicated　the　predominance　of　Nitrosomonas　and　the　absence　of　the　Nitrosospira　in　the　condition　of　insufficient　alkalinity,　which　was　consistent　with　the　SEM　results.　FISH　results　suggested　that　lack　of　alkalinity　presented　little　impact　on　the　relative　quantity　of　AOB.