Provided is an agent for treating and/or preventing obesity. An agent for suppressing expression of NPC1L1 (Niemann-Pick disease, type C1, gene-like 1) and/or LIPG (Lipase, endothelial) mRNA, and an agent for preventing and/or treating obesity, each comprising, as an active ingredient, a compound having CETP inhibitory activity, or a salt thereof, or a solvate thereof.