The purpose of this study is to develop the environment-friendly coolant. Cylindrical plunge grinding tests are carried out using alkaline electrolyzed water, high-frequency reduced water and alkali-reduced water as coolant. Most effective coolant is brought out in comparison with surface roughness, grinding force and workpiece surface temperature. Moreover, elemental analyses and measurements of contact angle of treated water are carried out in order to clarify the effect on grinding performance. Furthermore, elemental analyses and observation of evaporation residues in treated water are also carried out. As a result, grinding performance using alkali-reduced water is better than that using alkaline electrolyzed water or high-frequency reduced water.