Abstract: This paper describes the continuation of the previous laboratory work¹ on the observation of Radon and Thorium emanations from rock specimen under pressure. The equipments used in the experiment are nearly the same as before. The results show again the previous conclusion that the variation of radon content of underground water as a precursory phenomena of strong earthquakes is related to the fracturing of rock medium. However, for local regions, the characters of rock fracturing, of rocks themselves and so on are quite different so that the anomalous behavior of the variation of radon content before and after a strong earthquake may be quite different.