The　behavior　of　eighteen　concrete-filled　HSS　(hollow　structural　steel)　columns　with　or　without　fire　protection　after　exposure　to　the　ISO-834　standard　fire　subjected　to　axial　or　eccentric　loads　has　been　experimentally　investigated　and　the　results　presented　in　this　paper.　A　mechanics　model　is　developed　in　this　paper　for　concrete-filled　HSS　columns　after　exposure　to　the　ISO-834　Standard　Fire,　and　is　a　development　of　the　analysis　used　for　ambient　condition　(Han　et　al,　2001b).　The　predicted　load　versus　mid-span　deflection　relationship　for　the　composite　columns　is　in　good　agreement　with　test　results.　Based　on　the　theoretical　model,　influence　of　the　changing　strength　of　the　materials,　fire　duration　time,　sectional　dimensions,　steel　ratio,　load　eccentricity　ratio　and　slenderness　ratio　on　the　residual　strength　index　(RSI)　is　discussed.　It　was　found　that,　in　general,　the　slenderness　ratio,　sectional　dimensions　and　the　fire　duration　time　have　a　significant　influence　on　the　residual　strength　index　(RSI).　However,　the　steel　ratio,　the　load　eccentricity　ratio　and　the　strength　of　the　materials　have　a　moderate　influence　on　RSI.　Finally,　formulas　suitable　for　incorporation　into　building　code,　for　the　calculation　of　the　residual　strength　of　the　concrete-filled　HSS　columns　after　exposure　to　fire　are　developed　based　on　the　parametric　analysis　results.