The cell components of an iron-oxidizing F.ferrooxidans were analyzed with heterotrophic E.coli as a control group. The large amounts of total carbohydrate and lipids were represented in F.ferrooxidans and especially the total lipids including total sterol, glyceride, and phospholipid possessed about 4.6% of total dry cell. In amino acids analysis, an unknown metrial was detected in F.ferrooxidans nad it is assumed that material is a ninhydrin-positive and have an association with lipid.