(1) A number of strongly radioactive springs were discovered in Masutomi, Yamanasi Prefecture. (2) The radon content of a number of very small springs near spring A8 and A9 at Higurasi-no-huti was measured. On No. 88 day, spring A84 showed a content of 7130 Mache. On the same day the radon content of spring A9 (when the water sample was drawn with an injector from the inner part of the exit of the spring) registered 6870 Mache. (3) A strongly radioactive spring was discovered in Masutomi on No. 155 day, the radon content of which (spring A49, Dairokuten-no-izumi) is supposed to be always 3000 to 4000 Mache, although values higher than 5000 Mache were obtained at the time the sample was drawn, a small injector used. (4) The radon, chlorine, carbon dioxide contents, the amount of the flow and the water temperature, of spring A2 were measured daily during the period between No. 74 day and No. 89 day, and the effect of snow on the radon content, together with the chemical composition of the mineral springs was studied. The variation in the radon content of this spring is explained by assuming that the original mineral spring was diluted by thaw water. (5) The radon content of spring A9 was measured daily during the period between No. 1 day and No. 98 day. (6) The radon content of spring A9 fluctuated between 1030 and 1900 Mache during this period. (7) The radon content increases after snow or rain. (8) The higher the water temperature the higher the radon content (9) The variation in the chlorine, bicarbonate, and the carbon dio？ide contents were also measured daily during this period. (10) On No. 136 day, the radon content of spring A9 registered 12000 Mache. (11) In winter, on very cold and clear days after snow, the radon content is very low in the morning, increases in the day-time with the thawing of the frozen ground, and suddenly diminishes in the evening when the ground freezes again. (12) The radon content of frozen mineral water was measured. (13) [Rn/CO2] ratio in the mineral springs of Masutomi was dis？ussed. (14) It was very difficult ascertain any marked relation between the variations in the radon content of the mineral springs of Masutomi and the small earthquakes that occurred in Yamanasi Prefecture, during the period of this investigation. (15) The total analyses of spring A9 and spring A49 were intended. (16) A general survey of our investigation into the minute constituents of the mineral springs of Masutomi was made. (17) The chemical composition of the sinter of spring A6 is des？ribed.