(1) The author surveyed the environmental factors and the fauna of Sung-Yoo Cave(360m in length) from November 29 to December 2, 1961. (2) Air temperature, water temperature, moisture, water depth, water gravity, oxygen concentration carbon dioxide concentration and pH in water of the cave were studied as enveronmental factors. The results are shown in the Table 1~7 and Fig.3. (3) Four species of troglobite (22.2%). seven of troglophile(38.9%). four of troglozene(22.2%). and three of parasite constitute the terrestrial fauna of Sung-yoo Cave. In the other hand, all of the aquatic fauna(4 species of fish) of the cave were troglozene. (5) None of the species of animals listed in this paper has ever been recorded in Korea.