Abstract: The subject of this research is the problem of the finiteness of human existence within the framework of the philosophy of Russian cosmism. The article touches upon the theme of human perfection as an imperative factor of reaching immortality. The authors examine the two models of understanding of death and immortality within the philosophy of Russian cosmism in the context of comprehension of the phenomenon of perfection. The religious-philosophical and natural scientific models coexist in the Russian cosmism and divide cosmists into two factions; however, neither of the models fully reveal the possibility of the actual solution of the set by Russian cosmism tasks. Methodology of Russian cosmism implicates the need for the all-encompassing cognition of the world, studying of the subjects and occurrences in the process of their development and evolution, which potentially leads to the synthesis of the two diverse models of comprehension of the phenomena of death and immortality. The main conclusion lies in the statement that the philosophy of Russian cosmism on the assumption of achieving human immortality does not consider it outside the concept of perfection, but rather immortality is viewed as a result of reaching the human perfection. Depending on the model, there are differences in representations on the human perfection; but based on the methodology of the Russian cosmism, it is impossible to view a thing or occurrence in its relation to other thinks, cosmos, and its evolution. Thus, the path to solution of set by the Russian cosmism tasks lies in the synthesis of the two models, in other words, in synthesis of the religious-philosophical and natural scientific approach to the problem of death, immortality and human perfection.