Abstract: Metamorphosis is a motif often used in literary works. In his fairy tales, Andersen creatively connects the motif of metamorphosis with maturation. He presents the ethical dimension of humanity through metamorphosis and explores the meaning of growing up. Andersen creatively imbeds initiation ritual in transformation from animal-human hybrid to human being, connects human-to-animal transformation with the drive of socialization, and presents petrifaction as a metaphor of the termination of growing-up. By connecting metamorphosis with maturation, Andersen brings a new ethical dimension to this traditional motif, presenting growing-up as an ethical rebirth. From the perspective of ethical literary criticism, metamorphosis results from the change of Sphinx Factor, which is constituted by human factor and animal factor. Human factor, as a result of ethical choice, comes into being during the process of civilization, with moral consciousness as its core, while animal factor, the irrational one, is the legacy of human beings' animal ancestors, with desire at its central place. In fairy tales with metamorphosis motif, the protagonist can successfully transform to human being and, at the same time, grow up, when he or she becomes morally conscious and can restrain their irrational desire; if the protagonist surrenders to his or her desire, he or she will be changed into animal or inanimate being, with their maturation and socialization process terminated. With its ethical implication, in Andersen's metamorphosis fairy tales, maturation means to form an ethical identity, becoming morally conscious and capable of making ethical choice. Imbedding the ethical implication in metamorphosis, Andersen aims to set up model figures to help children understand the difference between man and animal, and thus guide their ethical choices.