Alkali-activated　slag　(AAS)　presents　a　promising　alternative　to　ordinary　Portland　cement　due　to　its　cost　effectiveness,　environmental　friendliness,　and　satisfactory　durability　characteristics.　In　this　paper,　cow　dung　waste　was　recycled　as　a　renewable　natural　cellulose　fiber,　modified　with　alkali,　and　then　added　to　AAS　mortar.　The　physico-chemical　characteristics　of　raw　and　modified　cow　dung　fibers　were　determined　through　Fourier　transform　infrared　(FTIR),　X-ray　diffraction　(XRD),　and　Scanning　electron　microscope　(SEM).　Investigations　were　conducted　on　the　dispersion　of　cow　dung　fibers　in　the　AAS　matrix,　as　well　as　the　flowability,　strength,　and　autogenous　shrinkage　of　AAS　mortar　with　varying　cow　dung　fiber　contents.　The　results　indicated　that　modified　fiber　has　higher　crystallinity　and　surface　roughness.　The　ultrasonic　method　showed　superior　effectiveness　compared　to　pre-mixing　and　after-mixing　methods.　Compared　with　raw　cow　dung　fibers,　modified　fibers　led　to　an　increase　of　11.3%　and　36.3%　of　the　28　d　flexural　strength　and　compressive　strength　of　the　AAS　mortar,　respectively.　The　modified　cow　dung　fibers　had　a　more　significant　inhibition　on　autogenous　shrinkage,　and　the　addition　of　2　wt%　cow　dung　fibers　reduced　the　7　d　autogenous　shrinkage　of　the　AAS　paste　by　52.8%　due　to　the　“internal　curing　effect.”　This　study　provides　an　alternative　value-added　recycling　option　for　cow　dung　fibers　as　a　potential　environmentally　friendly　and　sustainable　reinforcing　raw　material　for　cementitious　materials,　which　can　be　used　to　develop　low　autogenous　shrinkage　green　composites.　©　2023　by　the　authors.