Overpack in the engineered barrier (metal material such as carbon steel) adopted for the high level radioactive waste (HLW) geological disposal. Because it is buried deep underground in a chemically reducing atmosphere, the HLW geological disposal needs to get a long-term corrosion behavior test for carbon steel in the soil. In this study, we obtained data on the corrosion performed by microbes of the carbon steel using archaeological iron objects that had been buried in the soil for a long term. We chose archaeological iron objects excavated in Ibaraki, Japan and carried out a corrosion level examination according to a level system. The corrosion product of iron objects was also analyzed. The number of iron-reducing bacteria of the excavated iron objects of archaeological site was investigated by the most probable number method (MPN).The results show long-term corrosion behavior in the soil and it can be used to estimate the burial environment of overpack.