Hollow　structural　steel　(HSS)　columns　filled　with　concrete　offer　a　number　of　benefits　and　are　often　used　in　tall　buildings　and　other　industrial　structures.　A　mathematical　model　was　developed　and　used　to　investigate　the　influence　of　important　parameters　that　determine　the　fire　resistance　of　concrete-filled　hollow　steel　columns.　The　behavior　of　concrete-filled　HSS　columns　with　or　without　fire　protection　subjected　to　axial　or　eccentric　loads　was　experimentally　investigated　and　the　results　presented　in　this　paper.　The　parametric　and　experimental　studies　provide　information　for　the　development　of　formulas　for　the　calculation　of　the　fire　resistance　and　fire　protection　thickness　of　the　composite　columns.　The　main　objectives　of　this　work　were　threefold:　First,　to　report　a　series　of　fire　tests　on　composite　columns;　second,　to　analyze　the　influence　of　several　parameters,　such　as　the　sectional　dimension,　load　eccentricity　ratio,　and　fire　protection　thickness　on　the　fire　resistance　of　the　composite　columns.　It　was　found,　in　general,　that　the　sectional　dimension　and　the　fire　protection　thickness　have　significant　influence　on　the　fire　resistance　of　concrete-filled　HSS　columns;　however,　the　load　eccentricity　ratio　has　moderate　influence　on　the　fire　resistance.　The　final　objective　was　to　develop　formulas　for　the　calculation　of　the　fire　resistance　and　the　fire　protection　thickness　of　the　concrete-filled　HSS　columns.