It is believed that iron reducing bacteria can be active in a deep underground where the overpack will be placed, being in a reducing condition with less oxygen or anaerobic environment. A buffer material (such as bentonite) surrounding the overpack will react with groundwater to produce alkaline pore water. We need some information to judge whether the iron reducing bacteria would be a factor to promote the corrosion of the overpack if iron reducing bacteria inhabits in alkaline condition. Also, it is very important to evaluate effect of anions, which promote corrosion of the carbon steel on growth of iron reducing bacteria and on the corrosion behaviour of carbon steel. In this study, we conducted microbial corrosion experiments of carbon steel both in an alkaline liquid medium and in a liquid medium with anions. The results indicate that iron reducing bacteria can be active, even where it is in alkaline conditions with or without anions.