Abstract: A water-soluble metalworking fluid composition and a method of using the same. The water-soluble metalworking fluid composition has the components (A), (B), and (C), where (A) is a fatty acid having a carbon atom number of 9-11, (B) is an unsaturated fatty acid having a carbon atom number of 16-22, and (C) is a polymeric fatty acid having an acid value of 10-200 mgKOH/g. (A) is 1-20 mass %, (B) is 30-60 mass %, and (C) is 35-55 mass %, based on the total amount of the components (A), (B) and (C). The water-soluble metalworking fluid composition maintains the workability while improving the mechanical fouling.