In　order　to　use　biodegradable　organics,　produced　from　excess　activated　sludge　(EAS)　hydrolysis　and　acidification,　as　carbon　source　for　nitrogen　and　phosphorus　removal,　chemical　pretreatment　by　adding　NaOH　was　used　in　this　study　to　enhance　the　hydrolysis　efficiency　of　the　EAS.　Batch　experiments　were　conducted　at　ambient　temperature,　the　effect　of　sludge　characteristics,　initial　pH,　and　MLSS　on　the　SCOD　and　ORP　was　investigated.　It　was　found　that　SCOD　production　was　increased　with　the　increasing　of　the　pH,　the　optimal　pH　for　the　SCOD　production　is　11,　SCOD　concentration　was　reached　2322mg/L　after　10h　reaction　when　pH　at　11.　The　sludge　characteristic　have　an　important　effect　on　the　efficiency　of　activated　sludge　hydrolysis　and　acidification,　the　sludge　collected　from　A2/O　process　produced　the　highest　SCOD　(791mg/L)　compared　to　the　SBR,　step-feeding　(SF)　and　oxidation　ditch　(OD)　process.　SCOD　concentration　was　increased　with　the　MLSS　concentration　increasing,　which　was　increased　from　186mg/L　to　935mg/L　when　the　MLSS　increased　from　4000mg/L　to　10000mg/L.　Profiles　of　oxidation-reduction　potential　(ORP)　values　were　monitored　on-line,　model　covering　the　relationship　between　the　change　of　ORP　value　and　increase　in　SCOD　was　developed,　and　high　relativity　coefficient　was　achieved　(R20.85).　This　verified　that　the　ORP　monitoring　technique　is　not　only　useful　to　investigate　the　solubilization　rate　but　also　suitable　for　the　determination　of　optimal　solubilization　in　EAS　treatment.　©　2011　IEEE.