The　step-feed　sequencing　batch　reactor　(SBR),　a　novel　operation　mode　of　SBR,　was　used　for　the　study　of　nitrogen　removal　from　real　municipal　wastewater.　The　process　had　achieved　advanced　and　enhanced　nitrogen　removal　by　three　phases　of　consecutive　aerobic　and　anoxic　periods　and　also　three　steps　of　feeding,　combined　with　real-time　control.　The　control　strategies　utilized　pH　and　oxidation　reduction　potential　(ORP)　as　on-line　control　parameters,　especially　the　derivative　of　pH,　which　can　flexibly　control　the　durations　of　aerobic　and　anoxic　phases.　Moreover,　the　relationship　of　each　step　influent　flow　distribution　and　influent　C/N　was　discussed　in　this　paper,　which　there　was　a　unique　and　optimum　step　ratio　(lambda(opt))　for　the　wastewater　with　a　given　C/N　ratio.　Based　on　different　influent　C/N　ratios,　there　were　three　different　levels　of　step　ratio　(lambda),　that　is,　lambda　＜　1,　lambda　=　1,　and;　＞　1,　correspondingly　increasing　influent　flow　fill　mode,　equal　influent　flow　fill　mode,　and　decreasing　influent　flow　fill　mode.　In　this　study,　when　step　ratio　was　1.5　using　real　municipal　wastewater　as　influent　with　C/N　ratio　of　3.5,　the　lower　aeration　consumption　and　complete　denitrification　using　influent　as　carbon　source　could　be　achieved.　Nitrogen　removal　efficiency　could　be　greatly　improved　by　step　feeding　in　the　SBR,　total　nitrogen　in　the　effluent　was　lower　than　2　mg/L　and　the　average　TN　removal　efficiency　was　higher　than　98%,　while　only　requiring　small　amount　of　external　carbon　source.　(C)　2006　Elsevier　Inc.　All　rights　reserved.