The influence of iron-oxidizing bacteria, Thiobacillus ferrooxidans, grown in a ferrous ion-free medium, on the corrosion of type 304 stainless steel (UNS S30400) was evaluated. Electrochemical measurements were performed, both in the inoculate dandin the sterile media. Corrosion potential (Ecorr) for type 304 stainless steel exposed in the bacterial culture was shifted near +230 mVvs S. C.E. Cyclic voltammogram sshowed significant differences, a reduction peak was detected near -400 mV vs S. C.E. in the presence of the bacterial culture. This effect was most probably due to small quantities of Fe(III) compounds in the culture caused by iron-oxidizing bacteria. These results indicated that bacterial metabolic products affected the corrosion process, although they were able to cause initiation of corrosion of type 304 stainless steel. Keywords: stain less steel, corrosion potent ial, cyclic voltammetry ,microbially induced corrosion, iron-oxidizing bacteria