To　study　the　effect　of　future　seawater　intrusion　on　the　soil　organic　carbon　decomposition　in　tidal　freshwater　wetland，we　transferred　soil　samples　from　freshwater　tidal　wetland　to　brackish　tidal　wetland　in　the　Min　Estuary　of　southeast　China.　The　contents　of　soil　labile　organic　carbon（LOC）fractions　and　activities　of　carbon-acquiring　enzymes，including　1，4-glucosidase，cellobiohydrolase，peroxidase，and　phenol　oxidase，were　also　studied　after　30，180，and　510　days　of　soil　transfer.　Increased　soil　salinity　had　a　significant　impact　on　the　contents　of　soil　LOC　fractions.　The　increasing　soil　salinity　increased　soil　microbial　biomass　carbon　and　dissolved　organic　carbon　contents，and　decreased　soil　easily　oxidized　organic　carbon　contents.　As　salinity　increased，aboveground　plant　biomass　decreased　but　belowground　biomass　increased，fungal　abundance　increased，and　bacterial　abundance　decreased.　Activities　of　the　four　carbon-acquiring　enzymes　increased　as　soil　salinity　increased.　Correlation　and　regression　analysis　results　showed　that　carbon-acquiring　enzyme　activities　were　regulated　by　soil　Fe（III）/Fe（II）ratios，soil　carbon/nitrogen　ratios，and　soil　fungi/bacteria　ratios.　Overall，when　the　soil　salinity　increased　from　freshwater　to　oligohaline，plant　root　oxygen　loss　and　root　exudates　increased，and　the　quality　of　soil　organic　matter　became　worse.　These　changes　led　to　increases　in　soil　carbon-acquiring　enzyme　activities　and　decreases　in　soil　LOC　contents.　The　finding　indicates　that　rapid　sea-level　rise　in　the　future　will　lead　to　decline　of　soil　organic　carbon　storage　in　historical　tidal　freshwater　wetlands，and　the　ecosystem　function　will　be　threatened.　©　2023　Science　Press.　All　rights　reserved.