This paper presents an experimental investigation into the mechanical properties of YSt-310 cold-formed steel hollow sections, which is one of the most widely used structural steel in India, under steady state elevated temperatures ranging from approximately ambient to 800 °C. Elevated temperature stress–strain curves and reduction factors of key material parameters such as Young's modulus; yield stress; stresses corresponding to 0.5%, 1.5% and 2.0% strains; tensile strength and corresponding strain (%); fracture strain (%) and Ramberg-Osgood parameter are reported. Further, the reduction factors obtained from the current experimental programme are compared with predictions based on current fire design standards as well as those reported in literatures for cold-formed steel at elevated temperature. Statistical analysis was carried out to check the reliability of the elevated temperature reduction factors and it was found that the existing design rules are inaccurate and not applicable to cold-formed hollow steels at elevated temperature. A new set of fire design reduction factors are then proposed for cold-formed steels hollow sections based on lower bound values, considering both the current and previously reported experimental data. The newly proposed reduction factors are shown to offer improved mean (conservative) and reliable predictions and therefore recommended for inclusion in future revisions of fire design codes. © 2019