This　study　reported　a　＂treating　waste　by　waste＂　strategy　to　dispose　waste　activated　sludge　(WAS),　i.e.　reverse　osmosis　(RO)　brine-enhanced　anaerobic　fermentation.　RO　brine　was　hazardous　by-product　from　seawater　desalination　process,　which　contains　numerous　Na+.　After　4-day　RO　brine-enhanced　anaerobic　fermentation　at　Na+　concentration　of　0.33　mol/L,　5.0　g/L　VSS　reduction　(37.9%　of　VSS)　was　achievable,　leading　to　considerable　soluble　chemical　oxygen　demand　(SCOD)　release　of　349.6　mg/g　VSS.　Acetic　acid　was　predominant　component　in　SCOD　(31.1%),　followed　by　propionic,　butyric,　valeric　acids　and　proteins　(14.0-17.6%).　Sludge　solubilization　and　SCOD　composition　in　the　enhanced　anaerobic　fermentation　with　RO　brine　and　NaCl　agent　were　similar,　whereas　less　nutrient　release　and　extracellular　polymeric　substance　(EPS)　disruption　were　achieved　by　RO　brine,　attributing　to　the　Ca2+&Mg2+-caused　skeleton　strengthening　on　EPS　matrix.　Such　RO　brine-based　strategy　provided　environmental　and　economic　benefits,　e.g.　none　chemical　consumption,　synchronous　disposal　of　WAS　and　RO　brine.