In this work, the topographic features of the spatial pattern of biodiversity of the urban fauna in general in the city are revealed: the number of urban fauna species has a maximum in the southern part of the city and a minimum in the western part. The mammal fauna as a component of urban fauna in general exhibits greater plasticity and adaptability in relation to humans compared to other groups of biota, for example, the insect fauna and avifauna. The urban mammal fauna in Ulyanovsk has historically formed due to the penetration of representatives of various faunal complexes that inhabit the region into the city area and its vicinities: (1) floodplain species associated with the river Sviyaga and its tributaries, 36.17%; (2) forest species living in pine-deciduous, deciduous-pine, and taiga forests, 46.81%; (3) upland-steppe species associated with Cretaceous landscapes of the right bank, 6.38%; (4) steppe species, including mammals of the left bank, common for the native feather grass–fescue steppes, 6.38%. Some animal species have remained in the city and in the region due to their spread by humans—introduced species and species kept in fur farms (10.64%). Synanthropic species are associated with human settlements (4.26%). The occurrence of species in different zones of the city (right bank and left bank) and habitats with an increase in the level of urbanization and a decrease in species diversity (1–5) are as follows: (1) green zones—parks and squares with woody vegetation, 31 species; (2) floodplain of the river Sviyaga within the city, 24 species; (3) summer cottages within the city, 15 species; (4) private sector with one-storey buildings, 5 species; (5) multi-storey buildings, 4 species. In general, in an urban environment, mammal species that coexist with humans make up 66.19 % of the total number of mammal species in the region. At the same time, the number of rare mammal species listed in the regional Red Book is 12.68%. Thus, when conservation measures for the protection of animal habitats within the urban environment are observed, most species are able to maintain stable populations.