Ferredoxin is a type of electron carrier protein involved in many biological redox reactions and also incorporated as an electron transfer domain and subunit in redox enzyme complexes. MvhB-type polyferredoxin is an iron-sulphur protein composed of three to seven 2[4Fe-4S]-ferredoxin domains. In this short review, we introduce the structure and function of MvhB-type polyferredoxin modules in methanogenic enzymes and then discuss the possible physiological function of the putative MvhB-like polyferredoxins identified in microbial genomes.