The invention is directed to a composition for preparing a carbon dioxide external preparation characterized by comprising a substance generating an acid after being hydrolyzed, a carbonate, a thickener and water as essential components, and a composition for preparing a carbon dioxide external preparation characterized by comprising the essential components above, a gelating agent being gelated by a calcium ion and a water-insoluble or poorly soluble calcium salt. According to the invention, the carbon dioxide external preparation, which contains sufficient amount of carbon dioxide, from which the carbon dioxide is absorbed transdermally or transmucosally in a sustained manner, and which has a more potent cosmetic or medical effect, can be easily prepared. In addition, the composition for preparing a carbon dioxide external preparation with a low cost can be provided.