Concrete　filled　double　skin　steel　tubular　(CFDSST)　members　can　be　recognized　as　a　new　kind　of　concrete　filled　steel　tubular　(CFST)　construction.　They　consist　of　two　concentric　steel　tubes　with　concrete　sandwiched　between　them,　the　steel　tubes　can　be　circular　hollow　sections　(CHS),　square　hollow　sections　(SHS)　or　rectangular　hollow　sections　(RHS).　The　CFDSST　columns　have　almost　all　the　same　advantages　as　traditional　CFST　members.　Moreover,　they　have　lighter　weight,　higher　bending　stiffness,　and　have　better　cyclic　performance.　It　is　also　expected　that　CFDSST　columns　will　have　higher　fire　resistance　capacities　than　their　CFST　counterparts,　due　to　the　inner　tubes　of　the　former　being　protected　effectively　by　the　sandwiched　concrete　under　fire　condition.　In　the　past,　many　studies　have　been　performed　on　CFDSST　members　with　circular　or　square　sections.　However,　no　CFDSST　member　with　rectangular　section　was　investigated,　which　is　more　favorable　to　be　used　when　it　is　subjected　to　large　major-axis　bending　moment.　This　paper　studies　the　behavior　of　CFDSST　columns　where　both　inner　and　outer　tubes　are　RHS.　Theoretical　models　are　presented　to　predict　the　load-carrying　capacities　of　the　composite　members.