Modern infrastructure uses Hollow Steel Tube (HST) columns for high-rise buildings, bridges, and industrial structures due to its high strength-to-weight ratio, aesthetic appeal, and efficient material use. However, the performance of HST columns under fire conditions is a critical concern, as elevated temperatures can severely impact their structural behavior and durability, compromising structural integrity and safety. Understanding the post-fire behavior of these columns is essential for ensuring the sustainability of infrastructure subjected to fire hazards and contemplating the utilization of fire-damaged steel structures for subsequent rehabilitation or dismantling, considering the associated costs. Mild steel tube columns are readily available and widely used in construction, but there is limited research on their structural properties after a fire. This study aims to add to research on the structural behavior of mild steel tube columns post-deterioration after fire. In this research, Hot-rolled YST-240 HST stub columns are exposed to elevated temperatures (200 ℃, 400 ℃, 700 ℃, 900 ℃, and 1000 ℃) for 30, 60, and 90 min to determine their post-fire load-displacement response, peak load, and ductility. Results indicate that YST-240 HST columns can retain residual stiffness, strength, and ductility up to 400 ℃, with properties similar to those at ambient temperature, and remain usable at temperatures up to 700 ℃. Also, with increasing temperature, specimen ductility declines, except at 900 ℃, when it is highest. The findings of this research contribute to the development of fire-resistant structural designs.