Micromycetes are an integral part of the microbial community of cave ecosystems, they play the role of decomposers or lead a parasitic lifestyle. Microscopic fungi, including yeast, in caves are isolated from soil, air, water, mineral formations, rock surfaces and even troglobionts. By the ratio of fungi of different temperature regimes and the succession of species, one can inference the relationship between the underground cavity and the surface and the intensity of nutrient intake. Representatives of Chrysosporium, Mucor, Mortierella, Peniciliium, Trihoderma, Aspergillus, Geomyces predominate among microscopic fungi in caves. Micromycetes are actively involved in geochemical transformations of the environment, causing corrosion of rocks, which can pose a danger to the preservation of rock paintings in decorated cavities. Anthropogenic load leads to changes in the composition of microscopic fungi due to an increase in the trophic status of cave ecosystems, as well as due to the possible active transboundary transfer of microorganisms by visitors. The use of underground cavities as tourist sites dictates the need to develop criteria for standardizing the content of micromycetes in the air, taking into account the specifics of caves to ensure the safety of people. This review is aimed at summarizing the accumulated data on the diversity and distribution of microscopic fungi in karst caves.