Abstract: The present invention relates to a medium composition for the dedifferentiation of induced pluripotency stem cells, containing a phlorotannin fraction extracted and isolated from one type of brown algae selected from the group consisting of Ecklonia cava, Dictyopteris prolifera, Dictyota coriacea, Sargassum horneri, Ishige okamurai and the like. In addition, the present invention relates to a method for preparing induced pluripotency stem cells by using the medium composition. Induced pluripotency stem cells can be safely, easily and effectively prepared by using mesenchymal stem cells by using the medium composition of the present invention, and the prepared induced pluripotency stem cells can be differentiated into various cells, and thus can be useful as a cell therapeutic agent.