The paper deals with the stylistic device of "metamorphosis" and its functioning peculiarities in Selkup fairy tales and world mythology. During the analysis of folk and mythological plots the author determines the ways, reasons, character and motives of metamorphoses that happen with the characters. Metamorphoses that lead to the creation of animate as well as inanimate (toponyms, landscape parts) objects are considered. The modern interpretation of metamorphosis in the world literary tradition is analyzed.