The　proper　disposal　of　cow　dung　waste　has　always　been　a　great　challenge　for　the　agricultural　sector　in　China　and　around　the　world.　In　this　work,　the　cow　dung　was　processed　into　a　cheap　renewable　cow　dung　fiber　(CDF)　and　applied　into　cementitious　composites.　The　physicochemical　properties　of　raw　and　alkali　pretreated　CDF　were　analyzed　by　thermogravimetry,　Fourier　transform　infrared　spectroscopy,　X-ray　diffraction,　single　fiber　tensile　test　and　scanning　electron　microscopy.　The　strength　and　autogenous　shrinkage　of　cementitious　composites　reinforced　with　the　CDF　were　measured.　The　results　showed　that　alkali　pretreatment　dissolved　the　amorphous　components　(i.e.,　hemicellulose　and　lignin)　and　enhanced　the　crystallinity　of　cellulose.　The　pretreatment　of　CDF　by　1　mol/L　NaOH　solution　led　the　3　d　&　PRIME;s　compressive　and　splitting　tensile　strength　of　the　CDF　reinforced　cementitious　composites　to　increase　by　21.8%　and　12.5%,　respectively.　The　presence　of　CDF,　with　or　without　pretreatment　enabled　to　inhibit　the　development　of　autogenous　shrinkage　of　cementitious　paste.　This　work　is　expected　to　promote　an　alternative　application　for　the　recycling　of　cow　dung　waste　in　sustainable　building　materials.