The manual static chamber method, which is one of the most commonly used for measuring greenhouse gases (CH4, N2O and CO2) in rice paddy fields, has advantages which are easy installation and removal in the field and low manufacturing cost. Above all, it is advantageous to measure very small CH4 fluxes. However, the manual static chamber method may not capture the dynamic of CH4 fluctuation by varying factors on time scales and requires a lot of labor and has a limited sampling time and frequency. So far, many studies on CH4 measurement in rice paddies have been mostly limited to the manual static chamber method, and there was little research to reduce the uncertainty of chamber method. To overcome the disadvantages of the manual static chamber method, CH4 emitted from a chamber method were compared and evaluated through three methods; 1) auto-chamber system, 2) eddy covariance using micrometeorology, and 3) DNDC (DeNitrification – Decomposition) model. A. Comparison and evaluation CH4 emissions using auto-chamber and manual static chamber method As a result of evaluating CH4 emissions using manual chamber and auto-chamber, the total CH4 emissions between the two methods ranged from a minimum of 2.8% to maximum of 10.6%, but there was no significant difference. However, more minute changes of CH4 fluctuation by temperature were observed in the auto-chamber where the sampling frequency was fewer than the manual chamber. Measuring CH4 emission with an auto-chamber system is expected to reduce uncertainty and increase accuracy accompanied by labor reduction B. Comparison and evaluation CH4 emissions using eddy covariance and manual static chamber method In order to compare and evaluate CH4 emissions by eddy covariance and manual static chamber method, flux tower for eddy covariance and static chamber were installed for the investigation during two years in paddy field. The CH4 flux patterns by these two methods during rice growing season were similar, but the total CH4 emission measured by open-path method were 30% less than those of manual static chamber. The reason for the difference in CH4 emission were due to overestimation by manual chamber and underestimation by eddy covariance. The manual static chamber method can overestimates CH4 emissions due to environmental changes caused by high temperature and light interruption by acrylic partition in chamber. On the other hand, the open-path method for eddy covariance can underestimate its emission because it assumes negligible for density fluctuations and horizontal homogeneous terrain. C. Comparing and evaluation CH4 emissions using DNDC model and manual static chamber method As a result of evaluating CH4 emissions using DNDC model (simulated) and manual chamber (observed), the comparison of field observed and simulated daily CH4 fluxes with different treatments appeared that CF-NOM was the most closely matched among treatments. The results of statistics analysis showed that correlation (R2) was the best in CF-NOM (0.56), RMSE was the best in MD-NOM (1.29), and RSTD was better than both CF-NOM (0.84) and MD-NOM (0.84). The difference with total observed CH4 emission was higher in CF-OMS (-24.4%). The simulated emissions were underestimated compared with observed ones except MD-OMS. Nevertheless, by incorporating modifications based on the local weather, soil properties, and cultivation management, DNDC model could become a good tool for estimation of national GHGs emission in agriculture sector. The CH4 emissions on 15 locals level simulated by calibrated DNDC model were higher than the IPCC default and country specific emission factor because the various regional factors such as precipitation and soil texture were reflected as the input parameters.