Measurements of the natural propagation of UHF radio waves on an underground train are reported. Of prime interest are the natural propagation attenuation and the median signal level behavior. The propagation attenuation rates or the median signal level behaviors are found to correlate with the train carriages and frequency. On the front carriage, the propagation attenuation rate is 54 dB/100 m at 465 MHz and reduced to 21 dB/100 m at 820 MHz. However, on the rear carriage, it becomes 14.8 dB/100 m at 465 MHz and 7.8 dB/100 m at 820 MHz. It is shown that higher frequency is beneficial to the natural propagation and the train body greatly affects the natural propagation. Furthermore, the values of the path loss exponent are also given.