This study investigates the amplification effect on rooftop telecommunication towers in earthquakes. Two amplification factors are examined. One is the Height Amplification Factor (HAF), concerning acceleration increases along tower elevation; the other is the Resonance Amplification Factor (RAF), which magnifies vibration when natural frequencies of the tower and the building are close to each other. Two telecom buildings with rooftop tower are tested and analyzed using SAP2000. Recorded earthquake data are used to calibrate the SAP models so that a reliable damping model from the first building can be built. Based on this damping model, a second telecom building's ambient vibration is measured and analyzed to verify the accuracy of the SAP2000 model. The HAF and RAF of the rooftop tower in earthquake motions is studied for towers with different heights in the second building. The analytical results indicate that both amplification factors used in the current Taiwanese design guideline for rooftop telecom towers may be underestimated.