Diel and seasonal variations of CH4 flux from a paddy field were measured at Bang Khen Rice Experimental Station in Thailand. Diel measurement at the heading stage of rice plants showed that the daily average flux, amounting to 24.2 mg m-2hr-1, was equivalent to the flux measured in the late morning. The average values of seasonal variations of CH4 fluxes in 1992 major rice, 1993 second rice and 1994 second rice were 21.7, 4.3, and 6.7 mg m-2h-1, respectively*. The seasonal measurements in the second rice showed a relatively low CH4 emission, due to the very shallow water depth because of the limitation of the amount of irrigation water in the dry season. The results suggest that water supply is an important factor the evaluation of the global emission rates of CH4 from rice paddy fields.