This is an attempt to find out the periodicity of the natural hydrological phenomena by the function of vibration periodicity, under the assumption that the phenomena are periodic. The result of this study at Suwon is as follows: 1. Annual precipitation and tota1 precipitation during summer season have the periodicity of five years. 2. Annual temperature and tota1 temperature during winter season have the periodicity of seven years. 3. The regulation curve equations of the above vibration phenomena are as follows: a. Annual precipitation. Y=1149-250 cos2/5πt-33 sin 2/5t b. Total precipitation during summer season. Y=212′.9+33.06 sin (2/5πt+88°13′) c. Annual temperature. Y=140.3+3.3 sin (2/7πt+154°55′)