The Mase rice paddy site is a flux station in the AsiaFlux micrometeorological tower network. Located in a regularly cultivated rice paddy area of the Kanto plain in Japan, the site was established in 1999. The initial motivation was to quantify the energy and carbon balance in the rice paddy (ca, 54 a) where the tower was situated. Because of the accessibility and line-power availability, the site has involved many researchers and students from universities and institutes, broadening its target to studies on satellite and field remote sensing, ecosystem modelling, and nutrient cycling.