The effect of microbiological treatment of low-rank coal with an anaerobic microbial consortium on theirs characteristics and composition has been inwestigated. A large amount of pyrite sulfur is removed and coal ash is decreased with anaerobic conditions in closed flask. After biological treatment of these low-rank coals in a continuously operationg flow reactor without air blowiong and with everyday aeration, coal ash reduction is found to be more significant under conditions of reactor aeration due to activation of facultative microorganisems. In some time, some metals are removed from two kinds of low-rank coals, includiing iron, manganese, potassium, lithium, toxic and trace metals. The exchange of elements between coal and mineral culture medium depends on coal rank. Metal leaching is higher for higher rank coal.