This is the basic study of Cheong-song mineral waters(Dalgi and Sinchon) for a coagulant of Tofu. For comparison, $CaCl_2,;CaSO_4,;MgCl_2;and;MgSO_4$ are used as reference coagulants. The coagulability test was conducted by measuring the percentage transmittancy of filtered whey solution at 600 nm wavelength, in $80;{^{circ}C}$ and 10 mL of solution volume which composed of 2 mL of soy milk and coagulants. The coagulability test of mineral waters require more than an aliquot of 8 mL. Good result obtained by adding 0.4, 1, 0.8, 0.8 mL of reference coagulants and this is equivalent to the amount of 66.14, 232.83, 95.68, 78.88 mg of Ca and Mg respectively. The percentage transmittancy of filtered whey solution with added 8 mL of Dalgi and Sinchon mineral waters showed 50.74 and 58.52 respectively and the amount of mineral content of Ca and Mg equivalent to 2.41 and 2.48 mg respectively which is very lower value than the reference coagulants. This means mineral water has coagulation ability even in the low concentration.