Soil respiration is a critical pathway of carbon (C) cycling in terrestrial ecosystem. It is projected that the frequency and severity of forest pest outbreaks will increase as a consequence of increasing extreme climatic conditions. The outbreak of forest pests has been considered as one of the predominant natural disturbances affecting the C cycling of forest ecosystems. However, it remains unclear whether forest pest outbreaks will affect the emission of CO₂ from forest soils in the climatic transitional zone. Based on an outbreak of a defoliator (Lampronadata cristata and Ochrostigma albibasis) in a Quercus acutissima-Liquidambar formosana mixed forest on Jigong Mountain, we compared the soil respiration between the pest plague (2014) and the following normal year (2015), in order to determine the effects of the forest pest on soil CO₂ emission. We found that soil temperatures during July, August, September, and October in the pest plague year were 0.26 ℃, 0.51 ℃, 0.83 ℃, and 0.07 ℃ higher than those investigated in 2015, respectively, and soil respiration was increased by 129.9%, 77.1%, 61.6% and 58.9%. The mean soil respiration during the growing season in the pest plague year was 3.55 μmol m^-2 s^-1, which was 36.2% higher than that observed in the normal year (2.77 μmol m^-2 s^-1). The heterotrophic respiration during the growing season in pest plague year was 29.7% higher than that in the normal year. Therefore, the present study demonstrates that forest pest outbreaks can significantly increase soil CO₂ emissions at least in the short term. A better understanding of the effects of forest pests on forest ecosystems is needed for accurate estimations and modeling of terrestrial ecosystem C cycling.