In Yatsushiro area, the groundwater has been used as agricultural, industrial and dailylife water. The groundwater levels are rising recently. This is why the decrease of the population, the crop acreage of rice and rush, and the conserving water of the citizens and factories. In 2014, the removal of Arase dam has begun by the demand of the people to the local level. The circumstance of water resources in Yatsushiro area has changed apparently.In this paper, water qualities of the Kuma River and the groundwater of Yatsushiro area are investigated. The items of water qualities are ion analysis, conductivity and total residue. First of all, characteristic features of the water qualities of the Kuma River and the groundwater in Yatsushiro area are cleared up, and the relationship of the Kuma River and the groundwater is studied. It was proved that the groundwater in Yatsushiro is what the Kuma River water infiltrated. The characteristic features of the groundwater are different between left and right side of the Kuma River. It is found that there is the area that the concentration of chloride ion is over 800mg/l.