A recycling system for water-soluble coolant was developed. The interaction between water-soluble coolant and a cationic surfactant can remove the oil content as a suspended particle. The filtration with powdered activated carbon bed can recover a clear liquid from the surfactant treated coolant. The recovered water showed the almost same pH and Brix% as those of tap water unless a mass of microorganism was living in the recovered water. The water-soluble coolant can form a stable emulsion in the recovered water with a less amount of microorganism. The recycle coolant, which was diluted with recovered water with a less amount of microorganism, showed the same lapping force, removal rate and finishing surface roughness as those of virgin coolant in the lapping tests with S45C. However, an emulsion breaking occurred spontaneously in the recycle coolant diluted with recovered water with a mass of microorganism.