This　paper　presents　an　analytical　model　using　a　modified　space　truss　analogy　for　predicting　the　ultimate　torsional　capacity　of　reinforced　ultra-high-performance　concrete　(R-UHPC)　beams.　Both　solid　and　box　beams　are　considered.　The　credibility　of　the　proposed　model　is　evaluated　by　comparing　the　theoretical　predictions　of　the　ultimate　torsional　capacity　and　its　corresponding　twist　(Tu-αu)　to　experimental　results　of　several　R-UHPC　beams　(solid　and　box　beams)　available　in　the　literature.　The　results　are　also　compared　with　the　calculation　of　the　existing　models.　The　comparisons　show　that　the　proposed　model　gives　acceptable　predictions　of　the　ultimate　limit　torsional　capacity　of　R-UHPC　beams　and　the　corresponding　twist　angle　and　offers　better　accuracy　than　the　existing　analytical　models.　Additionally,　a　parametric　study　was　carried　out　to　determine　factors　that　influence　the　ultimate　torsional　capacity.　The　result　shows　that　the　ultimate　torsional　capacity　is　not　just　improved　by　the　increase　of　the　tensile　strength　of　UHPC　but　also　increased　by　the　increase　of　the　reinforcements　(transversal　and　longitudinal).　©　The　Author(s)　2022.