This study examined the FORMOSAT‐3/COSMIC radio occultation soundings of total electron content in the ionosphere (from 150 to 550 km) and refractivity index in the lower atmosphere (from 0 to 60 km) after/during the 2011 Mw9.0 Tohoku earthquake/tsunami. The refractivity index observations show the first evidence of the Tohoku earthquake/tsunami‐induced vertical oscillations in the lower atmosphere. The atmospheric oscillations with vertical wavelength ranging from 0.5 to 8 km and from 10 to 40 km, respectively, appear in the stratosphere and ionosphere after the earthquake onset. The short vertical wavelengths suggest that the oscillations are the atmospheric oscillatory tail due to the wavefront of the earthquake/tsunami. The radio occultation technique is a tool for detecting the atmospheric waves induced by earthquake or some other sources. Plain Language Summary It has been well known that the sudden uplift of the Earth's surface due to earthquake/tsunami significantly disturbs the upper atmosphere and ionosphere. However, the evidence of earthquake/tsunami‐induced waves in the lower atmosphere is insufficient due to the lack of observation supporting. Here the FORMOSAT‐3/COSMIC (F3/C) radio occultation refractivity index is for the first time to capture the Tohoku earthquake‐induced vertical oscillations at the stratosphere altitudes from 30 to 40 km. The results in this study not only shed lights on understanding of earthquake/tsunami waves perturbing the whole atmosphere but also suggest that the radio occultation technique can benefit to the earthquake/tsunami warning system. Key Points The study shows the first evidence of the Tohoku earthquake/tsunami‐induced vertical oscillations in the stratosphere Atmospheric oscillations with vertical scale range from 10 to 40 km and from 0.5 to 8 km, respectively, in the ionosphere and stratosphere The oscillations are mainly the atmospheric oscillatory tail due to the tsunami