PROBLEM TO BE SOLVED: To provide a differentiation-inducing agent composition of a white fat cell into a brown-like fat cell having excellent differentiation-inducing action of a white fat cell into a brown-like fat cell, which is a new effect not yet found in resveratrol, and being capable of being safely and inexpensively made and a pharmaceutical preparation and quasi drug containing the composition.SOLUTION: A differentiation-inducing agent of a white fat cell into a brown-like fat cell is characterized by heating resveratrol under alkaline conditions. A pharmaceutical preparation and quasi drug contain the composition.