Recent works on CH4 emissions from peatlands have demonstrated that ebullition can be a more important emission pathway than it has been thought. However, knowledge of its features and associated environmental factors is still very limited. In this study, we investigated the quantitative relationship between the amount of CH4 emitted via ebullition and changes in the atmospheric pressure through a laboratory experiment. During the flux measurement period, ebullition was recorded almost exclusively in air-pressure-declining phases. The increased volume of the gas bubbles due to reduction in atmospheric pressure and the amount of released gas bubbles revealed a strong linear relation, suggesting that in situ CH4 emissions via ebullition can be estimated using this correlation. Our results clearly showed that atmospheric pressure can be one of the most important factors to control CH4 emissions from peatlands and that ebullition can be the main transport mechanism during the pressure-falling phase.