The paper provides an ecological analysis of rare and endangered lichen species included in the Red Book of the Chuvash Republic. The new edition, published in 2020, includes information on 256 species of plants and fungi. The Red Book of the Chuvash Republic includes 30 species of rare and endangered lichen species, 14 species are included in the list of those which are subject to special attention and need constant monitoring in the natural environment. Biomorphological analysis has shown that rare lichen species belong to 3 types, 4 classes and 7 groups of life forms. The predominant species are bushy (bushy hanging group 11 species, bushy branching group 1 species, bushy erect group 1 species) and foliose (parted-lobed rhizoidal group 10 species, broad-bladed rhizoidal group 2 species) lichens. Ecological-substrate analysis has revealed that lichens included in the Red Book of the Chuvash Republic grow on 8 phorophytes (Tilia cordata, Quercus robur, Betula pendula, Salix cinerea, Pinus sylvestris, Picea abies, Abies sibirica, Populus tremula), on soil, on dead organic substrate and mosses. The greatest number of rare lichens was found on the bark of Tilia cordata, on the bark of Pinus sylvestris and on soil.