Provided are a naturally-derived agent for suppressing differentiation into adipocyte, readily available and ingestible in daily dietary life and having little side effects, a method for suppressing differentiation into adipocyte in a subject in need thereof, and the like. The present inventors have confirmed that a water extract of Sargassum horneri has the effect of suppressing differentiation from bone marrow mesenchymal stem cell into adipocyte, thereby accomplishing the present invention.
