The role of thermophilic sulphate-reducing bacteria (SRB) Desulfotomaculum geothermicum in mild steel corrosion was evaluated by electrochemical study and surface analysis technique. In the presence of D. geo- thermicum, the corrosion rate was 0.0698 mmpy at 50°C, which was higher when compared to control. Polarization study revealed that the bacteria enhanced cathodic reaction and suppressed anodic reaction. XRD data revealed that the presence of FeS enhanced the cathodic reaction by the formation of a protective film on the metal surface. Pitting was observed by confocal microscopy, which may be due to cathodic depolarization. The study implicates the importance of D. geothermicum in the corrosion of cooling towers of the petroleum refinery. damage caused or accelerated by the presence of bacteria and other microorganisms and their metabolic activities on metals and alloys. Many types of bacteria, including sulphate-, iron- and CO2-reducing bacteria, sulphur-, iron- and manganese-oxidizing bacteria are associated with the MIC of metals and alloys 1 . Among them, sul- phate-reducing bacteria (SRB) are recognized as a major group involved in anaerobic corrosion. These latter mi- croorganisms can coexist in naturally occurring biofilms with a wide bacterial community, including fermentative bacteria, often forming synergistic communities (consortia) that are able to influence electrochemical processes through cooperative metabolism 2 . The sulphate reductive activity of SRB is thought to account for >75% of the corrosion in productive oil wells, and for >50% of the failures of buried pipelines and cables 3 . SRB are strictly anaerobic microorganisms responsible for the terminal mineralization of organic matter in anoxic environments. They are a diverse group of prokaryotes that may be divided into four groups based on rRNA sequence analysis: Gram-negative mesophilic SRB, Gram-positive spore-forming SRB, thermophilic bacterial SRB and thermophilic archael SRB 4