The object of the present invention is to provide PPAR.gamma. ligand derived from naturally occurring sources and a composition for preventing and/or improving Insulin Resistance Syndrome, diabetes mellitus, obesity or visceral fat obesity comprising the PPAR.gamma. ligand as an active agent.The present invention relates to a ligand for peroxisome proliferator-activated receptor which comprises curcumin or its derivatives. The composition according to the present invention, which comprises the PPAR.gamma. ligand as an active agent is useful for preventing and/or improving Insulin Resistance Syndrome, diabetes mellitus, obesity or visceral fat obesity.