Multiculturalism, which was formed as a result of the synthesis of heterogeneous aboriginal population with migrant one was and remains a key feature of the resettlement community of eastern Russia. When and how this diversity began to be perceived as ethnic» («national» in Russia's tradition), what is the dynamics and basic characteristics of this process under conditions of radical social and political changes in the country, part of which was and still is Siberia? The authors formulate the problem in terms of the process of «ethnicization». To what degree ethnicity as a property of the urban space is inherent of siberian cities, which partly transformed on the base of the elements of the pre-Soviet imperial space, partly developing as a purely Soviet project? What are functions of ethnicity and ethnicization of urban space in the life of the late- and post-Soviet city? The phenomenon of ethnicization, its causes and mechanisms, as well as the specifics of its manifestations in the resettlement community of eastern Russia are equally important and interesting in the within this point of view. The authors believe that the process of ethnicization, i. e. actualization of the ethnic factor in everyday life, social and political relations, in the mechanism of the formation of social networks and relationships, their marking by the ethnic categories, began during the decay of estate relations in the late imperial period. World War I and the Civil War accelerated this process. It acquired new forms and scales as a result of «national policy» of Soviet power in the framework of various «national projects», the initiator and the main actor of which was the state. According to authors’ opinion, transition from «ethnicization» as a state project to self-development process became the main difference of post-Soviet era. Ethnicization becomes the result and feature of a number of political, social, economic and demographic processes that have their own logics and dynamics.