Adding　short　steel　fibers　into　slag-based　geopolymer　mortar　and　concrete　is　an　effective　method　to　enhance　their　mechanical　properties.　The　fracture　properties　of　steel　fiber-reinforced　slag-based　geopolymer　concrete/mortar　(SGC/SGM)　and　unreinforced　control　samples　were　compared　through　three-point　bending　(TPB)　tests.　The　influences　of　steel　fiber　volume　contents　(1.0%,　1.5%　and　2.0%)　on　the　fracture　properties　of　SGC　and　SGM　were　studied.　Load-midspan　deflection　(P-d)　curves　and　load-crack　mouth　opening　displacement　(P-CMOD)　curves　of　the　tested　beams　were　recorded.　The　compressive　and　splitting　tensile　strengths　were　also　tested.　The　fracture　energy,　flexural　strength　parameters,　and　fracture　toughness　of　steel　fiber-reinforced　SGC　and　SGM　were　calculated　and　analyzed.　The　softening　curves　of　steel　fiber-reinforced　SGC　and　SGM　were　determined　using　inverse　analysis.　The　experimental　results　show　that　the　splitting　tensile　strength,　fracture　energy,　and　fracture　toughness　are　significantly　enhanced　with　fiber　incorporation.　A　strong　correlation　between　the　equivalent　and　residual　flexural　strengths　is　also　observed.　In　addition,　the　trilinear　strain-softening　curves　obtained　by　inverse　analysis　predict　well　of　the　load-displacement　curves　recorded　from　TPB　tests.