Previous　studies　have　demonstrated　that　sludge　hydrolysis　and　short-chain　fatty　acids　(SCFAs)　production　were　improved　through　NaCl　assistant　anaerobic　fermentation.　However,　the　effect　of　NaCl　concentrations　on　hydrolase　activity　and　microbial　community　structure　was　rarely　reported.　In　this　study,　it　was　found　that　α-glucosidase　activity　and　some　carbohydrate-degrading　bacteria　were　inhibited　in　NaCl　tests,　owing　to　their　vulnerability　to　high　NaCl　concentration.　Correspondingly,　the　microbial　community　richness　and　diversity　were　reduced　compared　with　the　control　test,　while　the　evenness　was　not　affected　by　NaCl　concentration.　By　contrast,　the　protease　activity　was　increased　in　the　presence　of　NaCl　and　reached　the　highest　activity　at　the　NaCl　concentration　of　20　g/L.　The　protein-degrading　and　SCFAs-producing　bacteria　(e.g.,　Clostridium　algidicarnis　and　Proteiniclasticum)　were　enriched　in　the　presence　of　NaCl,　which　were　salt-tolerant.　©　Copyright　©　2020　Pang,　Xin,　He,　Cui,　Guo,　Liu,　Yan,　Liu,　Wang　and　Nan.