To improve dispersibility of fine particles, uniform wetting, and adhesion to a wire and a workpiece, prevent rising of temperature and sticking of a grain, facilitate water washing, by an action of gel member included in a base, and enchance accuracy and working performance in a worked surface.

This working fluid for wire cutting of the hard-to-cut material comprises (A) 0.05 to 5% aqueous solution of sodium polycarboxylate whose molecular weight is 550 to 9,000,000, and (B) a fine particle of silicon carbide, and has a weight ratio of (A) to (B)=1:0.11 to 2.0. Component (A) has specific gravity of 0.9 to 1.7, viscosity of 2 to 10,000 mPa.s, and pH of 7 to 10. The working fluid for surface grinding of the hard-to-cut material comprises (A) the aqueous solution as described above, and (B) a fine particle selected from any of diamond, corundum, silicon carbide, boron nitride, zirconia, zircons, chromium oxide, and cerium oxide or a mixture of at least two fine particles of the above substances, and has a weight ratio of (A) to (B)=1:0.01 to 2.0. (A) has specific gravity of 0.9 to 1.7, viscosity of 2 to 10,000 mPa.s, and pH of 7 to 10.