It is necessary from sanitary point of view that water for swimming pool is kept free from germs, and disinfectants containing chlorine have been widly used for this purpose. Recently, a novel disinfectant composed of neutral salt of calcium hypochlorite was developed in Japan, and the large tablet being especially suitable for disinfection of swimming pool water has been marketed since last year. In order to establish a sanitary control method of swimming pool water with the product, experiments on both continuous charge method and direct throw method of the tablets were conducted at the municipal swimming pool in Takada, Niigata-prefecture, over one swimming season. It was proved that the above mentioned methods are satisfactory to the purpose.