Concrete-filled　stainless　steel　tubular　(CFSST)　columns　combine　the　advantages　of　composite　action　seen　in　concrete-filled　steel　tubular　(CFST)　columns　with　the　durability　benefits　associated　with　stainless　steel.　An　effective　means　of　reducing　the　material　usage　in　the　outer　stainless　steel　tube　in　CFSST　columns　is　to　embed　an　inner　carbon　steel　profile.　This　enables　the　material　costs　to　be　reduced,　while　achieving　similar　load-bearing　capacity　and　durability,　as　well　as　enhanced　fire　resistance.　The　behaviour　of　such　steel　reinforced　composite　columns,　i.e.　concrete-filled　stainless　steel　tubular　(CFSST)　columns　with　outer　square　cross-sections　and　embedded　carbon　steel　profiles,　under　ISO　834　standard　fire　conditions　is　investigated　in　this　study　by　finite　element　(FE)　analysis.　Firstly,　FE　models　are　developed　and　validated　against　relevant　published　experimental　data　on　CFSST　and　steel　reinforced　CFST　columns　under　fire　conditions.　Based　on　the　validated　FE　models,　the　working　mechanisms　of　the　studied　steel　reinforced　CFSST　columns　under　fire　conditions　are　investigated　by　analysis　of　the　temperature　field,　failure　modes,　axial　deformation　versus　time　response　and　internal　force　distribution.　The　fire　performance　of　the　studied　steel　reinforced　CFSST　columns　is　also　evaluated　in　comparison　with　CFST　and　CFSST　columns　with　the　same　total　cross-sectional　area　of　steel　or　the　equivalent　cross-sectional　load-bearing　capacity　at　ambient　temperature.　Finally,　with　respect　to　fire　resistance,　the　optimal　ratio　of　the　cross-sectional　areas　of　the　inner　carbon　steel　profile　to　the　outer　stainless　steel　tube　is　investigated.