Water soluble coolant has been widely used as machining fluid owing to its environment- friendly characteristic, fine protection property and low price. However, as this type of coolant is perishable, a large amount of labor is required for its maintenance of the coolant. Moreover, in high precision machining, separation of minute machined chips generated during grinding and machine oil from the coolant is indispensable, and a special filtering-device and other equipments are necessary. In this paper, a method to purify water-soluble grinding fluid using PGA based flocculant was examined. As a result of experiments, it was clarified that the suspended matters such as grinding swarf or free abrasive grains in the fluid can be removed at the collection rate of more than 99%. A new filter-less coolant purification technology was established by combined use of micro bubble coolant.