This　paper　describes　an　experimental　study　on　the　flexural　and　eccentric　compressive　behavior　of　concrete-filled　square　steel　tube　(CFSST)　beam-columns　stiffened　with　PBL　stiffeners.　Three　types　of　CFSST　beam-columns　were　fabricated　and　tested　under　the　flexural　moment　and　eccentric　compressive　load.　Among　the　three　types　of　columns,　the　two　types　of　columns　were　strengthened　with　the　PBL　and　steel　plate　stiffeners;　the　other　type　of　columns　was　not　strengthened.　In　addition,　extensive　finite　element　analyses　(FEA)　were　carried　out　to　evaluate　the　stress　distribution.　Flexural　test　results　show　that　failure　modes　of　specimens　without　stiffeners　were　different　from　specimens　with　the　PBL　or　steel　plate　stiffeners.　The　results　also　demonstrate　the　distribution　of　cracks　in　the　concrete　was　affected　by　stiffeners　and　the　columns　with　the　PBL　stiffeners　have　the　most　uniformed　crack　distributions.　The　capacity　improved　by　the　PBL　stiffeners　was　insignificant.　However,　the　flexural　stiffness　of　the　specimen　stiffened　with　the　PBL　stiffeners　was　about　20%　larger　than　the　unstiffened　specimen.　Eccentric　compressive　load　test　results　show　the　capacity　of　specimen　with　the　PBL　stiffeners　was　6.95%　larger　than　the　unstiffened　specimen.　The　eccentric　compressive　capacity　decreased　with　the　increase　of　the　eccentricity　ratio　or　slenderness　ratio.　FEA　results　show　that　stiffeners　can　effectively　improve　the　mechanical　behavior　of　CFSST　specimens　under　bending　and　eccentric　compressive　loads.