The article presents the results of studies aimed at characterictics of quantitative and qualitative composition of aboriginal consortium of microorganisms from coal mines dumps of Lviv-Volynsky coal-basin with different storage time. The defined qualitative composition of substrates' microbiocenosis does not depend on the storage time, be cause it builds up in a course of substrates' formation and is defined by already estab lished chemical and mineralogical composition of the dumps. It was confirmed that heterotrophic and acidophilic chemolithotrophic bacteria, namely mesophilic and mode rately thermophilic genera Acidithiobacillus and Sulfobacillus, are present in the ab original consortium of substrates from coal mines dumps. Isolation of the acidophilic chemolithotrophic bacteria from substrates with neutral pH (from the dumps under study) proves that spreading of these bacteria is much wider than that of naturally aci dic ecosystems. It was stated that the neutrophilic thionic and sulphate reducing bacteria are present in the composition of the microbial association of the studied dumps. The existence of sporulated "silicate" bacteria capable of breaking quartz in the heterotro phic component of microbiocenosis was also confirmed. The study proved that repre sentatives of different groups of microorganisms of the aboriginal microbiota prevail quantitatively in the dumps with long storage time. This is a consequence of substrates' transformations in a course of storage under the exposure to exogenous factors that, in their turn, leads to a greater display of biocenosis in the substrates.