Guandushi Forest Ecosystem Station is one of the long-term ecological research networks of Taiwan (TERN) and is located at 700m to 1700m above sea level in central Taiwan. The sampling site of this study is in the 35 years old Cunninghamia lanceolata plantation. We measured the CO2 flux from the soil and δ13 CPDB values and concentration of organic carbon to investigate the source and the flux of CO2. Measurements of soil CO2 were made on surface with litters and organic rich layer removed. The measurements were made periodically at different seasons, over daytime and during the nighttime for over a period of about 2 years. Root and soil δ13CPDB values and carbon concentrations were made on a series of organic soil samples from a soil profile of 160cm depth. The CO2 fluxes range from about 9 to 24 mole CO2/m2/month and are higher in warm season and daytime than in cold season and at night, respectively. The integrated flux is 1240 g C/m2/year. For comparison, the carbon storage in pedon is 29783 g C/m2. The concentration of the soil organic carbon ranged from 0.55 to 3.55% and relatively constant except the surface samples which are very high (10.4%). δ13CPDB values range from -24.0 to -27.3 per mil with the 13C enriched samples located at mid-section (20 to 100cm). δ13CPDB values of the soil samples generally differ from that of the plant material of the forest, except for the surface samples.