In　this　paper,　the　structural　behavior　of　concrete-filled　double　steel　tubular　(CFDST)　stub　columns　composed　of　square　hollow　sections　is　investigated　experimentally　and　numerically.　The　experimental　program　comprises　compression　tests　on　short　columns　loaded　concentrically.　The　test　parameters　mainly　focused　on　the　influences　of　the　width-to-thickness　ratios　of　steel　tubes　and　concrete　strength　on　the　axial　behavior　of　CFDST　stub　columns.　Finite　element　(FE)　models　are　also　developed　to　investigate　the　influences　of　a　wide　range　of　structural　parameters　on　their　axial　performance.　It　is　observed　that　square　CFDST　columns　have　improved　strength　and　ductility　compared　to　their　CFST　and　DCFST　counterparts.　Finally,　a　calculation　formula　is　proposed　to　predict　their　ultimate　compressive　strengths　under　the　axial　compression　load.