The Namsan Ecological Tower Site based on a flux tower was equipped with eddy covariance and automatic opening/closing chamber systems to collect long-term continuous measurements of CO2 flux, such as the net ecosystem exchange (NEE) and soil CO2 efflux in a cool-temperate Quercus mongolica forest. The mean concentrations of atmospheric CO2 (705 mg/m3) during the summer were smaller than those measured (770 mg/m3) during the winter. The mean CO2 flux during the summer period was negative (-0.34 mg m-2s-1), while that during the winter period was positive (0.14 mg m-2s-1). CO2 was deposited from the atmosphere to the surface in the summer. The daily mean value of soil CO2 efflux increased from spring to summer. The seasonal pattern in the rate of soil CO2 efflux tightly followed the seasonal pattern in soil temperatures. The Q10 values for soil CO2 efflux varied in a range from 2.12 to 3.26, and increased with increasing soil depth. The maximum value of total carbon uptake (i.e., NEE) during the growing season was -8 g CO2 m-2 day-1. At the same time, the rate of soil CO2 efflux was 6.9 g CO2 m-2day-1. The amplitude of flux variations in NEE was approximately 14% larger than those in soil CO2 efflux. These results suggest that in cool-temperate regions of the Korean peninsula, the forest ecosystem of Q. mongolica may have a larger atmospheric CO2 uptake, due primarily to its high photosynthetic capacity and low ecosystem respiration.