The resi Its of investigation of speleothem (moonmilk) from the Snezhnaya cave (West Caucasus, Abkhazia) are-reported. The structure of microbial complexes from moonmilk was investigated by quantita- tive PCR; strains of culturable microorganisms were isolated and their preferred temperature and carbon sources were determined. Among eubacteria, -34% belonged to the iron bacteria (Rhodoferax). Most bacte- rial strains were shown to be facultative psychrophiles with the maximum growth rate at 4C. The microstruc- ture and elemental composition of mionmilk were investigated using a scanning electron microscope (EVO- 40HV, Carl Zeiss) and silicon drifi X-ay detector X-MAX 80 ffM2' The visually plastic and homogeneous mass of moonmilk was shown to be highly heterogeneous, containing various microstructures. The elemental composition of some nanostructures depended on the structure of bacterial biofilms. Some loci of the biofilm were found to contain up to 46% (wt/wt) of iron oxides. Calcium content was high, up to 61.5% (wt/wt) only in cubic crystalline structures which were not involved in microbiological processes.