Volatile　fatty　acids(VFAs)　are　suitable　carbon　sources　for　nitrogen　and　phosphorus　removal.　A　large　amount　of　VFAs　can　be　produced　in　the　alkaline　fermentation　process　of　WAS.　Temperature　and　sludge　concentration　are　two　critical　factors　for　waste　activated　sludge　(WAS)　fermentation,　therefore　the　effect　of　temperature　and　sludge　concentration　on　hydrolysis　and　acidification　of　WAS　was　investigated　at　15°C,　35°C　and　pH=10　under　anaerobic　condition.　The　results　showed　that　soluble　chemical　oxygen　demand　(SCOD)　production　yields　were　impacted　little　by　sludge　concentration.　Low　or　high　sludge　concentrations　were　disadvantage　for　acid　production,　the　best　sludge　concentration　for　acid　production　was　VSS=8.54　g/L.　At　any　sludge　concentration　investigated,　acetic　acid　dominated　in　the　six　volatile　short　chain　fatty　acids　produced　by　sludge　fermentation,　besides　the　percentage　of　acetic　acids　were　higher　at　low　sludge　concentration　than　high　sludge　concentration.　Temperature　impacted　significantly　on　the　hydrolysis　of　WAS　with　higher　sludge　concentration,　but　it　impacted　significantly　on　the　acidification　of　WAS　with　lower　sludge　concentration.　Medium　sludge　concentration　at　6.832,　8.540　g/L　influenced　little　on　ammonia　release　at　15°C　and　35°C,　sludge　concentration　influenced　more　significantly　on　phosphorus　release　at　35°C　than　at　15°C.