Effects　of　aspect　ratio　and　volume　fraction　of　straight　steel　fiber　on　the　modulus　of　elasticity　(MOE),　compressive　strength,　and　flowability　of　ultra-high-performance　concrete　(UHPC)　were　investigated.　The　results　show　that　the　MOE　and　compressive　strength　of　UHPC　increase　and　the　flowability　of　the　fresh　UHPC　decreases　with　the　increase　of　fiber　volume　and　fiber　aspect　ratio.　Steel　fiber　has　both　positive　and　negative　effects　on　the　MOE　of　UHPC.　The　positive　effect　of　steel　fiber　is　due　to　the　high　elastic　modulus　of　steel　fiber　itself.　The　negative　effect　is　caused　by　the　decrease　of　the　MOE　of　UHPC　matrix　due　to　the　decrease　of　the　flowability　of　fresh　UHPC　and　the　increase　of　the　porosity　and　the　inner　defects　after　the　fibers　adding　into　the　matrix.　A　semi-empirical　formula　was　proposed　for　predicting　the　MOE　of　the　UHPC　based　on　the　experimental　data,　comprehensively　considering　the　positive　and　negative　effects　of　fibers.　It　is　indicated　that　the　MOE　of　the　UHPC　could　be　strongly　correlated　to　the　compressive　strength.　©　2020,　Editorial　Department　of　Journal　of　the　Chinese　Ceramic　Society.　All　right　reserved.