Abstract: Studies on CO₂ exchange between vegetation and atmosphere can enhance the scientific understanding and modelling of carbon budget on terrestrial ecosystem.As a part of the ChinaFLUX program, CO₂ flux was measured for year-round in 2003 by an open-path eddy covariance system over a broadleaved Korean pine forests in northeastern China.The net ecosystem carbon exchange(NEE) between forest and atmosphere ranged from(-6.37) to 2.13 g/(m²·d) during the observational year, with the net carbon assimilation peak occurred in June, and a highest net carbon efflux occurred in October.The nocturnal NEE showed an exponential regression relationship with 5 cm depth soil temperature, and the CO₂ respiration Q₁₀ of ecosystem was 3.17.With the increase of photosynthetic active radiation(PAR), CO₂ flux changes were in well accordance with the curve of Michaelis-Menten model.The total NEE was -191.3 g/m² in 2003, which indicated that the broadleaved Korean pine forests of Changbaishan Mountains were functioning as a moderate carbon sink.