O-Saek mineral well is located in Yang-Yang county, Kang Won province and known as a famous well because of its special taste and air bubble. Some villager say that it has a treating ability on the gastrointestinal disorder. Authors intended to clarify wether this mineral well has any special ingredients and could be drunk as potable water. The result were as follow: 1. There wasn`t any bacteria and contamineous organic substances. 2. Alkalinity was 1,624 ppm owing to calcium ingredient in the ground. 3. Acidity was 344 ppm which value shows the existance of free carbon dioxide in water. 4. Free carbon dioxide was measured as high as 302.7 ppm. 5. Iron 4.0 ppm, manganese 0.3 ppm were detected and these material would be key factor making special taste. 6. Copper wasn`t observed but authors think forward reexamination is necessary to detect some heavy metals which may be exist.