Uniaxial　tensile　behavior　is　the　important　character　for　studying　resistivity　and　toughening　effect　of　engineering　cementitious　composites　(ECC).　Uniaxial　tensile　test　of　three　ratios　UF　cellulose　fiber　reinforced　cementitious　composites　(UF-ECC)　and　the　influence　regularity　on　the　mechanical　properties　of　ECC　under　different　fiber　content　is　studied　in　this　paper.　The　relationship　of　crack　width　and　tensile　stress　is　researched.　Tensile　fracture　energy　and　characteristic　length　are　discussed.　The　result　indicates　that　from　0.3%　to　0.6%　of　UF　cellulose　fiber　in　volume,　maximum　tensile　strain,　fracture　energy　and　characteristic　length　for　UF-ECC　respectively　improve　183%,　419%　and　281%.　The　maximum　strain　of　UF-ECC　is　8-20　times　more　than　that　of　polypropylene　fiber　reinforced　concrete.　UF　cellulose　fiber　has　good　resistivity　and　toughening　effect,　and　significantly　improves　the　cracking　resistance　and　deformability　for　ECC.　ECC　can　show　strain-hardening　and　multiple　cracking　performances　in　uniaxial　tensile　test.