This　study　investigated　the　flexural　behavior　of　rectangular　ultra-high　performance　concrete-filled　high-strength　steel　tube　(CuFTh)　members.　A　total　of　11　tests　were　conducted.　The　influence　of　yield　stress　of　steel　(Fy),　steel　fiber　volume　content　of　UHPC　(ρ),　height　(H)　of　steel　tube,　and　thickness　of　steel　tube　wall　(t)　was　investigated.　3D　finite-element　models　were　developed　and　benchmarked　to　conduct　parametric　studies.　Results　from　the　experimental　tests　and　FEM　analyses　indicated　that:　(i)　Fy,　t,　and　H　have　a　significant　influence　on　the　flexural　strength,　while　the　compressive　strength　of　concrete　has　a　negligible　impact;　and　(ii)　increasing　ρ　slightly　improves　the　flexural　strength,　but　obviously　reduces　the　ductility.　Additionally,　results　from　the　experimental　tests　and　FEM　analyses　were　compared　with　the　strength　estimated　using　AISC　360-16,　GB　50936-2014,　Eurocode　4,　and　AIJ.　The　comparisons　showed　that　Eurocode　4　and　AISC　360-16　can　reasonably　estimate　the　flexural　strength　of　rectangular　CuFTh　members.　AIJ　is　recommended　for　predicting　the　service-level　flexural　stiffness　of　rectangular　CuFTh　members.　©　2023