The water samples of 55 springs of Misasa were analysed in the years 1950～1951. The temperatures of the waters ranged from 44° to 85° C. Radon content ranged from 34.1 to 2360×10(-10) curies per liter. pH 6.2～7.5. Evaporation residue: 534～1940 mg/kg. K(+) :10.4～47.3mg/kg. Na(+) : 140.4～574mg/kg. Ca(2+) : 7.56～49.06mg/kg. Mg(2+) : 0.11～15.3mg/kg.. Fe(2+) : 0.10～0.67mg/kg. Cl(-) : 138～854mg/kg. SO(4)(2-) : 29.2～187mg/kg. HCO(3)(-) : 74.8～370mg/kg. HBO(2)(-) : 1.80～19.6mg/kg. S(2)O(3)(2-) : o.62～3.69mg/kg. Radon sources seem to exist at shallow places under the ground and the radon in the thermal wacer is supposed to have been derive partly from the ground water which also contains considerable amount of radon. A close linear correlation (r=0.751) was proved between the sulfate and the chloride ion contents.