During the past decade, researches on the behavior of steel columns at elevated temperature have been carried out experimentally and theoretically. Most of the works were focus on the critical temperature of steel columns under specified service load or the fire resistance duration of protected steel columns in fire conditions. The knowledge related to the ultimate strength of unprotected steel columns is limited. With the advancement of metal production and environmental concern, a new type of structural steel, Fire-resistant steel (FRS), has been developed to conquer inherent weakness of conventional steel at elevated temperature. The requirement of fire-protection used in the fire-resistant steel columns can be reduced or even lifted as compared to conventional steel columns. In order to adopt the fire resistance design of steel structures into the performance-based design, the ultimate strength of steel columns at different temperature levels is needed. A series of steel columns, including the columns made from conventional steel and fire-resistant steel, was loaded to fail under specified temperature to investigate the structural behavior of steel columns under fire conditions. This is attempted to establish the reduction effects of column strength resulting in the increasing temperature. Based on the research results, a design guideline is proposed to determine the buckling curves of steel columns under fire events.