Abstract: Production of electricity by microorganisms is a new interesting subject which has received high attention by researchers, industries and NASA. In Microbial fuel cells (MFC) electricity is generated via microbial activities. It is proposed that waste materials as sewage, food leftovers and basically all sorts of biodegradable organic matters have the capability to be used in MFC. These devices are harmless to the environment. Basically wide range of bacteria can be used as candidates in MFC. Basic structure, mechanism of action, types of microorganisms and chemical reactions are discussed in this paper.