We measured the net ecosystem CO2 exchange (NEE) in an alpine meadow ecosystem (latitude 37¿29'--45'N, longitude 101¿12'--23'E, 3250 m above sea level) on the Qinghai-Tibetan Plateau throughout 2002 by the eddy covariance method to examine the carbon dynamics and budget on this unique plateau. Diurnal changes in gross primary production (GPP) and ecosystem respiration (Re) showed that an afternoon increase of NEE was highly associated with an increase of Re. Seasonal changes in GPP corresponded well to changes in the leaf area index and daily photosynthetic photon flux density. The ratio of GPP/Re was high and reached about 2.0 during the peak growing season, which indicates that mainly autotrophic respiration controlled the carbon dynamics of the ecosystem. Seasonal changes in mean GPP and Re showed compensatory behavior as reported for temperate and Mediterranean ecosystems, but those of GPPmax and Remax were poorly synchronized. The alpine ecosystem exhibited lower GPP (575 g C m-2 y-1) than, but net ecosystem production (78.5 g C m-2 y-1) similar to, that of subalpine forest ecosystems. The results suggest that the alpine meadow behaved as a CO2 sink during the 1-year measurement period but apparently sequestered a rather small amount of C in comparison with similar alpine ecosystems.