Volatile　fatty　acids　(VFAs)　are　essential　for　removing　biological　nitrogen　and　phosphorus　in　wastewater　treatment　plants.　The　purpose　of　this　work　was　to　investigate　whether　and　how　the　addition　of　NaCI　could　improve　the　production　of　VFAs　from　waste　activated　sludge　(WAS).　Sludge　solubilization　was　efficiently　improved　by　the　addition　of　NaCI.　Both　protein　and　carbohydrate　in　the　fermentation　liquid　increased　with　the　dosage　of　NaCI,　and　it　provided　a　larger　amount　of　organic　compounds　for　the　production　of　the　VFAs.　NaCI　had　inhibitory　effects　on　the　production　of　methane　and　a　high　dosage　of　NaCI　could　severely　suppress　the　growth　of　methanogens,　which　decreased　the　consumption　of　the　VFAs.　Consequently,　the　production　of　VFAs　was　significantly　enhanced　by　the　addition　of　NaCI.　The　maximum　production　of　VFAs　was　achieved　with　the　highest　dosage　of　NaCI　(3316　mg　(COD)/L　at　the　NaCI　dosage　0.5　mol/L;　783　mg　(COD)/L　without　the　addition　of　NaCI).　Therefore,　this　study　indicates　that　using　NaCI　could　be　an　efficient　method　for　improving　the　production　of　VFAs　from　WAS.　(C)　2015,　The　Society　for　Biotechnology,　Japan.　All　rights　reserved.