Abstract: In this study, the influence of the Tibetan Plateau and the Rocky Mountains on ENSO variability is investigated using a fully coupled climate model. Compared to that in the real world, the amplitude of ENSO variability becomes larger after removing the Tibetan Plateau or the Rocky Mountains. The ENSO amplitude is considerably stronger in a world without the Tibetan Plateau than that without the Rocky Mountains. The ENSO variability is closely linked with the mean climate in the tropical Pacific. The removal of the Tibetan Plateau results in weakened trade winds, an eastward shift of the atmospheric convection center, a shallower mixed layer depth, and an El Niño-like sea surface temperature (SST) distribution. These mean climate changes result in enhanced wind-stress sensitivity, Ekman upwelling sensitivity, and thermocline sensitivity, finally leading to a 60% increase in the ENSO amplitude. However, without the Rocky Mountains, the tropical Pacific shows a more complicated trade wind change, with a slight eastward shift of the atmospheric convection center, a deeper mixed layer depth, a flattened thermocline, and a La Niña-like SST distribution. These mean climate responses strengthen the wind stress and thermocline sensitivities, leading to a 10% increase in the ENSO amplitude. This study suggests that the uplift of the Tibetan Plateau and the Rocky Mountains during the geological period has played an important role in suppressing the ENSO variability.