Although Xishuangbanna is within the tropics, it has large seasonal climatic variations. Paddy soil has substantial effects on carbon cycle. The CO2 exchange between paddy soil and atmosphere, and the factors influencing this exchange have both become important issues for global carbon\|cycle research. Using the static opaque chamber and gas chromatography technique, CO2 emission from paddy soil and its affecting factors were investigated in Xishuangbanna, SW China. In this study, soils with and without rice plants at three nitrogen fertilization levels (N0, N150 and N300) were examined. We found that diurnal variation of ecosystem respiration could be modeled with single peak curve throughout the rice\|growing season. The maximum and minimum emission rates occurred between 11:00 ~13:00 and at 0:00, respectively. There was a significant correlation between CO2 emission rates and air temperature. Different nitrogen fertilizer levels had the same pattern of ecosystem or soil respiration. Soil respiration varied seasonally, significant at the 1% level. The maximum value occurred during fallow season post\|harvest stage, minimum in the growing season and intermediate in the fallow season before rice transplanting. Soil moisture and temperature were the dominant factors influencing soil respiration. When the soil moisture was below 34%, there was positive linear relationship between soil moisture and soil respiration rate. When soil moisture exceeded 38%, there was an exponential relationship between soil respiration and temperature significant at the 1% level. Throughout the growing season, soil or ecosystem respiration rates under different nitrogen fertilizer levels did not differ, except that the N300 treatment reduced plant respiration. In the short term, nitrogen level increased soil respiration rates. The annual estimated soil respiration was 6.27 t C hm-2,6.31 t C hm-2 and 5.89 t C hm-2 for the N0, N150 and N300 treatments, and the annual net fixation CO2\|C from the atmosphere was 1.41 t C hm-2,2.22 t C hm-2 and 1.11 t C hm-2. Therefore paddy soil in Xishuangbanna serves as a carbon sink at all fertilizer levels.