In Misasa there occur only few weak sulfur springs, their　maximum hydrogen sulfide content being about 5mg per liter. The ground of Misasa consists of granite and there is no active volcano in the vicinity. So the author tried　to explain the mechanism of the occurrence of sulfur spring in Misasa by a reaction of the primarily alkaline　thermal water upon pyrite. Namely: XFeS(2) + 3Na(2)C(O)3 = 2Na(2)S(1-5) + Na(2)S(2)O(3) + 3CO(2) + XFeS(1-2) Thiosulfate in sulfur spring waters should not be taken for a secondary product from hydrogen sulfide as accepted generally, but is most probably a primary product to the latter. The phenomenon of white turbidity in sulfur spring　is caused mainly by the sulfur liberated from the polysulfide decomposed by the change in pH and temperture of thermal waters and not by the sulfur liberated from the　oxidation of hydrogen sulfide. Some experimental data were　shown to support the theory．