Methane flux from rice paddies and methane concentration in soil water at rice paddies were measured weekly through rice growing season of 4 years from 1991 through 1994. Methane flux and methane concentration in the soil water changed through each growing season as well documented by many researchers. In addition, the seasonal patterns of change, as well as total methane emission from rice paddy, varied year to year. The seasonal change and its difference among years were not completely explained with air temperature nor soil temperature. However, assuming that methane emission from rice paddy is driven by diffusion through rice plants, four year data showed that the conductance of rice plants for methane diffusion had wide ranges, and suggested that the conductance was highly dependent on air temperature or soil temperature.