Co-seismic groundwater-level and temperature changes caused by the Mw9.0 Japan earthquake in Chinese mainland are described.The recorded water-level changes were mostly oscillations,with some step decreases mostly in the coastal area of Southeast China and step increases mostly in Northeast China and the North-South Seismic Belt.The water-temperature changes were mainly decrease with slow recovery in Sichuan-Yunnan,South China,and lower reaches of Jiangzhong,and sharp increase followed by sharp decrease,or vice versa,in North China and Northeast China.For wells that showed step changes in both water level and temperature,more showed them in the same direction than in the opposite direction.