In order to investigate the distribution of an iron-oxidizing bacterium, Ferrobacillus ferrooxidans in Korea, the authors had carried out the chemical and microbiological analysis of mine water. The results obtained were as follows : 1. Ferrobacillus ferrooxidans concerned to leaching was isolated from 10 copper mine water out of 46 sites in Korea. 2. As the results of bacterial oxidation, the contents of sulfuric acid, ferric sulphate and copper in the bacteria-bearing solutions were higher than those in bacteria-free solutions.