Bonding　performance　between　steel　fiber　and　cement　matrix　is　critical　for　the　stress　transformation　and　crack　control,　which　significantly　affects　the　mechanical　properties　of　ultra-high　performance　concrete　(UHPC).　To　enhance　the　fiber/matrix　bond,　this　study　proposed　a　microbiological　technique　to　pretreat　the　steel　fiber　surface　via　microbially　induced　calcite　precipitation　(MICP)　treatment.　MICP　generates　calcium　carbonate　(CaCO3)　crystals　bonded　on　the　surface　of　steel　fiber,　leading　to　an　increase　in　roughness　and　hydrophilicity.　The　results　obtained　from　single　steel　fiber　pullout　tests　indicate　that　the　bond　strength　and　pullout　energy　of　steel　fiber　are　both　increased　by　MICP　treatment.　The　good　bonding　consequently　resulted　in　more　residual　hydration　products　attached　to　the　fiber　surface　after　the　pullout　test.　The　tests　on　the　UHPC　samples　with　untreated　and　treated　fiber　confirmed　the　benefits　of　MICP　treatment　in　improving　the　mechanical　properties　of　UHPC.　It　is　demonstrated　that　MICP　treatment　on　steel　fiber　can　increase　the　compressive　and　flexural　strength　of　UHPC　by　∼16%　and　∼50%,　respectively.　©　2022　Elsevier　Ltd