Dissolved　oxygen　(DO)　concentration　profiles　were　characterized　during　the　aerobic　organic　substrate　removal　phase　in　a　sequencing　batch　reactor　(SBR)　for　the　treatment　of　a　chemical　industrial　wastewater.　In　the　initial　stage　(0-10　min),　DO　concentration　rose　sharply　to　a　peak　level.　Subsequently,　the　DO　was　slowly　decreased　and　approached　a　plateau　during　the　COD　removal　phase.　When　the　organic　substrate　was　consumed,　the　DO　concentration　rose　sharply　from　the　previous　plateau.　This　was　an　indication　of　the　end　of　the　COD　removal　phase,　and　showed　an　inflection　point　on　the　DO　profile.　At　a　fixed　aeration　rate,　the　initial　peak　DO　concentration　was　related　to　the　initial　COD　concentration.　The　initial　COD　can　be　estimated　based　on　on-line　monitoring　of　the　initial　DO　data.　Changing　the　aeration　rate　to　control　DO　at　a　proper　level　(about　2　mg/L)　during　the　initial　stage　(10　min)　not　only　ensures　oxygen　supply　and　saves　aeration　energy,　but　also　simplifies　operational　management.　A　method　of　fuzzy　control　of　the　aeration　rate　using　on-line　DO　monitoring　was　developed.　The　inflection　point　on　the　DO　profile　can　be　used　as　an　indication　to　terminate　aeration.　Fuzzy　control　of　the　aeration　rate　and　aeration　duration　for　COD　removal　was　constructed　based　on　the　DO　profile.　Test　results　with　the　fuzzy　control　demonstrated　an　improved　treatment　efficiency　by　35%　and　saved　aeration　energy　by　50%　in　comparison　with　that　without　fuzzy　control　when　COD　removal　was　85-90%.