In recent years, concrete-filled box columns (CFBCs) have been commonly used in high-rise buildings. In particular, steel box columns filled with high-performance concrete (HPC) are more common than concrete-encased steel columns. However, a number of fire test results show that there are significant differences between HPC and normal concrete after being subjected to high temperatures. Therefore, the residual strength of HPC-filled box columns exposed to fire was determined in this study. Two groups of full-size specimens were fabricated. The specimen of the control group was loaded at room temperature to achieve its ultimate load. On the other hand, fire tests were carried out on three specimens of the experimental group to investigate their residual-load-bearing capacity after exposure to elevated temperatures (400, 600, and 800 °C). To monitor and measure the temperature of the CFBC specimens during the fire test, an appropriate number of thermocouples were buried inside and outside the column. The thermocouples can effectively measure the temperature of the CFBC specimens during the fire test. The test results show that the residual ultimate strength of CFBC specimens increased at 400 and 600 °C by 5.2 and 1.0% respectively, compared with room-temperature strength. However, with a further increase in temperature to 800 °C, the residual ultimate strength was 15.7% lower than that of the control group at room temperature.