In　general,　the　calculation　of　ultimate　load　capacity　(UL)　of　a　concrete-filled　steel　tubular　(CFST)　column　is　based　on　the　assumption　that　the　load　is　resisted　by　both　the　steel　tube　and　the　concrete　core　simultaneously　as　a　composite　member.　However,　steel　tubes　of　CFST　columns　are　preloaded　due　to　self-weight,　wet　concrete　weight　as　well　as　temporary　construction　loads　before　the　composite　action　is　formed.　There　is　still　no　consensus　on　how　the　preload　affects　the　loading　resistance　of　CFST　columns　and　how　to　quantify　the　effect　of　preload　on　the　ultimate　strength.　The　paper　reported　an　experimental　study　on　circular　CFST　columns　subjected　to　preload.　The　testing　results　showed　that　the　preloading　effect　increased　with　the　increase　of　slenderness,　decreased　the　ultimate　load　capacity　and　increased　the　deformation　significantly　at　high　preloading　ratio,　but　did　not　have　much　influence　on　the　ultimate　load　capacity　at　light　preload.　Then,　a　parametric　analysis　of　coupled　effects　of　preloading　ratio　with　other　parameters,　such　as　slenderness　ratio,　eccentric　ratio,　as　well　as　material　properties,　is　presented.　Finally,　a　simplified　method　is　proposed　to　predict　the　ultimate　load　capacity　of　CFST　columns　with　preload.　The　preloading　reduction　factor　of　simplified　methods　of　UL　based　on　regressive　analysis　can　be　used　to　evaluate　the　UL　of　CFST　columns　with　preload　after　verified　by　overall　comparison　of　total　preloading　tests.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.