The article is devoted to problems of cultural security of frontiers. The object of the research is comparison of southern Russian and Siberian frontiers. The subject of the study is the problem of cultural safety in the frontier regions. The methodology of study is J. Turner’s theory who was the creator of the concept of the American frontier. The article considers the peculiarities of the frontiers of Siberia and Southern Russia, identifies their common features, such as heterogeneity, intentionality, competition for resources, religious conflicts, unstable borders, borderland position, lifestyle free from traditions, etc. The analysis of the conquest history of the Southern regions and Siberia allows us to draw conclusions about the nature of the development process of the Russian metropolis, the peculiarities of the colonization process from the surrounding region. The analysis of the history and theory of frontiers shows that these areas largely remain marginal, unstable, causing threats to the cultural security in these regions. In the modern period, South-Russian and Siberian frontiers show signs of re-frontier, forming the border aimed at Russia’s developing by its neighbors (countries in the Caucasus, Central Asia in southern China and in Siberia).