The Equatorial Atmosphere Radar (EAR) is located at the equator (0.20¿S, 100.32¿E) in West Sumatra, Indonesia. The capability of the EAR to observe short-term variations of the tropopause altitude is shown. Near the tropopause, the EAR receives strong echoes caused by the rapid increase of hydrostatic stability with altitude. By applying this characteristic, the radar tropopause (RT) was determined. The RT agreed well with both the lapse-rate tropopause (LRT) and the cold-point tropopause (CPT) in altitude with a time resolution of 3 hours. The power spectrum of the RT altitude from 1 July to 18 December, 2001 showed a clear 1-day peak. The amplitude of its diurnal cycle as revealed in composites is as small as ~0.1 km. Nevertheless, the RT was able to reproduce the diurnal cycle in the LRT and the CPT well, which indicates that the EAR can observe short-term variations of the tropical tropopause.