Ferritic　stainless　steel　achieves　a　lower　and　steady　price　level　due　to　low　nickel　content　compared　to　duplex　and　austenitic　stainless　steels.　Accordingly,　the　combination　of　ferritic　stainless　steel　tube　and　concrete　will　have　better　application　prospects　in　corrosive　marine　environments.　However,　the　structural　application　of　concrete-filled　ferritic　stainless　steel　tube　(CFFSST)　members　is　still　limited　due　to　the　absence　of　performance　data　and　design　guidelines.　Accordingly,　this　paper　aims　to　comprehensively　investigate　the　behaviour　of　eccentrically　loaded　concrete-filled　rectangular　ferritic　stainless　steel　tubular　(CFRFSST)　slender　columns　using　the　nonlinear　finite　element　(FE)　method,　and　develop　a　suitable　design　method.　Two　different　material　models　were　introduced　to　simulate　corner　and　flat　regions　of　rectangular　ferritic　stainless　steel　tube.　Good　consistency　was　found　between　the　simulation　and　experimental　results　against　the　failure　mode,　ultimate　load　and　moment,　and　axial　load　versus　mid-height　deflection　curves　for　eccentrically　loaded　CFRFSST　slender　columns.　This　is　followed　by　the　mechanism　analysis　and　parameter　study　of　the　studied　CFRFSST　columns,　which　revealed　that　the　longitudinal　stress　and　Mises　stress　show　significant　changes　perpendicular　to　the　loading　line　direction,　while　there　is　almost　no　change　along　the　loading　line　direction.　In　addition,　the　initial　stiffness　and　ultimate　load　increased　by　increasing　the　cross-sectional　aspect　ratio,　yield　stress　and　concrete　strength,　while　they　decreased　as　the　eccentricity　ratio,　slenderness　ratio　and　width-to-thickness　ratio　increased.　The　outputs　of　the　FE　analysis　and　existing　experimental　results　were　used　to　examine　the　applicability　of　current　design　codes　for　designing　the　studied　CFRFSST　columns.　The　results　demonstrated　an　unexpected　deviation　generated　in　the　design　predictions.　At　the　end,　a　new　design　method　for　eccentrically　loaded　CFRFSST　slender　columns　was　proposed　which　achieved　better　predictive　consistency.　©　2024　The　Authors