In this thesis, Japanese mythology is compared with Polynesian mythology. Particularly, two Polynesian myths are selected as comparative material. The first one is a Maori cosmogony myth, a South Island version of Tāne, the second one a Samoan trickster myth, The Octopus and the Rat. Tāne is compared with the Japanese cosmogony myth, while The Octopus and the Rat is compared with the Japanese trickster myth, the White Rabbit of lnaba. Some common elements between the two mythologies and their origins are discussed in an analysis of the myths. Both myths are also translated into Japanese. To my knowledge, this is the first time this version of Tāne and The Octopus and the Rat have been translated into Japanese. Present Polynesian and Japanese migration theories and studies are also investigated, in order to explain the occurrence of similarities between both mythologies.