Sequence　hybrid　biological　reactor　(SHBR)　was　proposed,　and　some　key　control　parameters　were　investigated　for　nitrogen　removal　from　wastewater　by　simultaneous　nitrification　and　denitrification　(SND)　via　nitrite.　SND　via　nitrite　was　achieved　in　SHBR　by　controlling　demand　oxygen　(DO)　concentration.　There　was　a　programmed　decrease　of　the　DO　from　2.50　mg.L-1　to　0.30　mg.L-1,　and　the　average　nitrite　accumulation　rate　(NAR)　was　increased　from　16.5%　to　95.5%　in　3　weeks.　Subsequently,　further　increase　in　DO　concentration　to　1.50　mg.L-1　did　not　destroy　the　partial　nitrification　to　nitrite.　The　results　showed　that　limited　air　flow　rate　to　cause　oxygen　deficiency　in　the　reactor　would　eventually　induce　only　nitrification　to　nitrite　and　not　further　to　nitrate.　Nitrogen　removal　efficiency　was　increased　with　the　increase　in　NAR,　that　is,　NAR　was　increased　from　60%　to　90%,　and　total　nitrogen　removal　efficiency　was　increased　from　68%　to　85%.　The　SHBR　could　tolerate　high　organic　loading　rate　(OLR),　COD　and　ammonia-nitrogen　removal　efficiency　were　greater　than　92%　and　93.5%,　respectively,　and　it　even　operated　under　low　DO　concentration　(0.5　mg.L-1)　and　maintained　high　OLR　(4.0　kg　COD.m(-3).d(-1)).　The　presence　of　biofilm　positively　affected　the　activated　sludge　settling　capability,　and　sludge　volume　index　(SVI)　of　activated　sludge　in　SHBR　never　hit　more　than　90　ml.g(-1)　throughout　the　experiments.